CA2217723C - Metallic glass alloys for mechanically resonant marker surveillance systems - Google Patents

Abstract

A glassy metal alloy consists essentially of the formula: Fe a Co b Ni c M dB
e Si f C g, where "M" is at least one member selected form the group consisting of molybdenum, chromium and manganese, "a-g" are in atom percent, "a" ranges from about 30 to about 45, "b" ranges form about 4 to about 40, "c" ranges from about 5 to about 45, "d" ranges from about 0 to about 3, "e" ranges from about 10 to about 25, "f" ranges from about 0 to about 15 and "g" ranges from about 0 to about 2. The alloy can be cast by rapid solidification into ribbon, annealed to enhance magnetic properties, and formed into a marker that is especially suited for use in magneto-mechanically actuated articles surveillance systems. Advantageously, the marker is characterised by relatively linear magnetization response in the frequency regime wherein harmonic marker systems operate magnetically. Voltage amplitudes detected from the marker are high, and interference between surveillance systems based on mechanical resonance and harmonic re-radiance is virtually eliminated.

Description

METALLIC GLASS ALLOYS FOR MECHANICALLY
RESONANT MARKER SURVEILLANCE SYSTEMS

BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates to metallic glass alloys; and more particularly to metallic glass alloys suited for use in mechanically resonant markers of article surveillance systems.

2. Description of the Prior Art Numerous article surveillance systems are available in the market today to help identify andJor secure various animate and inanimate objects.
Identification of personnel for controlled access to limited areas, and securing articles of merchandise against pilferage are examples of purposes for which such systems are etriployed.
An essential component of all surveillance systems is a sensing unit or "marker", that is attached to the object to be detected. Other components of the system include a transmitter and a receiver that are suitably disposed in an "interrogation" zone. When the object carrying the marker enters the interrogation zone, the functional part of the marker responds to a signal from the transmitter, which response is detected in the receiver. The information contained in the response signal is then processed for actions appropriate to the application:
denial of access, triggering of an alarm, and the like.

Several different types of markers have been disclosed and are in use. In one type, the functional portion of the marker consists of either an antenna and diode or an antenna and capacitors forming a resonant circuit. When placed in an electromagnetic field transmitted by the interrogation apparatus, the antenna-diode marker generates harmonics of the interrogation frequency in the receiving antenna. The detection of the harmonic or signal level change indicates the presence of the marker. With this type of system, however, reliability of the marker identification is relatively low due to the broad bandwidth of the simple resonant circuit. Moreover, the marker must be removed after identification, which is not desirable in such cases as antipilferage systems.
A second type of rriarker consists of a first elongated element of high magnetic permeability ferromagnetic material disposed adjacent to at least a second element of ferromagnetic material having higher coercivity than the first element.
When subjected to an interrogation frequency of electromagnetic radiation, the marker generates harmonics of the interrogation frequency due to the non-linear characteristics of the marker. The detection of such harmonics in the receiving coil indicates the presence of the marker. Deactivation of the marker is accomplished by changing the state of magnetization of the second element, which can be easily achieved, for example, by passing the marker through a dc magnetic field.
Harmonic marker systems are superior to the aforementioned radio-frequency resonant systems due to improved reliability of marker identification and simpler deactivation method. Two major problems, however, exist with this type of system: one is the difficulty of detecting the marker signal at remote distances. The amplitude of the harmonics generated by the marker is much smaller than the amplitude of the interrogation signal, limiting the detection aisle widths to less than about three feet. Another problem is the difficulty of distinguishing the marker signal from pseudo signals generated by other ferromagnetic objects such as belt buckles, pens, clips, etc.

Surveillance systems that employ detection modes incorporating the fundamental mechanical resonance frequency of the marker material are especially advantageous systems, in that they offer a combination of high detection sensitivity, high operating reliability, and low operating costs. Examples of such =
systems are disclosed in U.S. Patent Nos. 4,510,489 and 4,510,490 (hereinafter the '489 and '490 patents).
The marker in such systems is a strip, or a plurality of strips, of known length of a ferromagnetic material, packaged with a magnetically harder ferromagnet (material with a higher coercivity) that provides a biasing field to establish peak magneto-mechanical coupling. The ferromagnetic marker material is preferably a metallic glass alloy ribbon, since the efficiency of magneto-mechanical coupling in these alloys is very high. The mechanical resonance frequency of the marker material is dictated essentially by the length of the alloy ribbon and the biasing field strength. When an interrogating signal tuned to this resonance frequency is encountered, the marker material responds with a large signal field which is detected by the receiver. The large signal field. is partially attributable to an enhanced magnetic permeability of the marker material at the resonance frequency. Various marker configurations and systems for the interrogation and detection that utilize the above principle have been taught in the '489 and '490 patents.
In one particularly useful system, the marker material is excited into oscillations by pulses, or bursts, of signal at its resonance frequency generated by the transmitter. When the exciting pulse is over, the marker material will undergo damped oscillations at its resonance frequency, i.e., the marker material "rings down" following the termination of the exciting pulse. The receiver "listens"
to the response signal during this ring down period. Under this arrangement, the = surveillance system is relatively immune to interference from various radiated or power line sources and, therefore, the potential for false alarms is essentially eliminated.

A broad range of alloys have been claimed in the '489 and '490 patents as suitable for marker material, for the various detection systems disclosed.
Other metallic glass alloys bearing high permeability are disclosed in U.S. Patent No.
4,152,144.
A major problem in use of electronic article surveillance systems is the tendency for markers of surveillance systems based on mechanical resonance to accidentally trigger detection systems that are based an alternate technology, such as the harmonic marker systems described above: The non-linear magnetic response of the marker is strong enough to generate harmonics in the alternate system, thereby accidentally creating a pseudo response, or "false" alarm. The importance of avoiding interference among, or "pollution" of, different surveillance systems is readily apparent. Consequently, there exists a need in the art for a resonant marker that can be detected in a highly reliable manner without polluting systems based on alternate technologies, such as harmonic re-radiance.

SUMMARY OF INVENTION

The present invention provides magnetic alloys that are at least 70% glassy and, upon being annealed to enhance magnetic properties, are characterized by relatively linear magnetic responses in a frequency regime wherein harmonic marker systems operate magnetically. Such alloys can be cast into ribbon using rapid solidification, or otherwise formed into markers having magnetic and mechanical characteristics especially suited for use in surveillance systems based on magneto-mechanical actuation of the markers. Generally stated the glassy metal alloys of the present invention have a composition consisting essentially of the formula Fea Cob Ni,_ Md B~ Sif Cg , where M is selected from molybdenum, chromium and manganese and "a", "b", "c", "d", "e", "f' and "g" are in atom percent, "a" ranges from about 30 to about 45, "b" ranges from about 4 to about 40 and "c" ranges from about 5 to about 45, "d" ranges from about 0 to about 3, "e" ranges from about 10 to about 25 , "f' ranges from about 0 to about 15 and "g" ranges from about 0 to about 2. Ribbons of these alloys, when mechanically resonant at frequencies ranging from about 48 to about 66 kHz, evidence relatively linear magnetization behavior up to an applied field of 8 Oe or more as well as the slope of resonant frequency versus bias field close to or exceeding the level of about 400 Hz/Oe exhibited by a conventional mechanical-resonant marker.
Moreover, voltage amplitudes detected at the receiving coil of a typical resonant-marker system for the markers made from the alloys of the present invention are comparable to or higher than those of the existing resonant marker. These features assure that interference among systems based on mechanical resonance and harmonic re-radiance is avoided The metallic glasses of this invention are especially suitable for use as the active elements in markers associated with article surveillance systems that employ excitation and detection of the magneto-mechanical resonance described above.
Other uses may be found in sensors utilizing magneto-mechanical actuation and its related effects and in magnetic components requiring high magnetic permeability.
BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description of the preferred embodiments of the invention and the accompanying drawings in which:
Fig. 1(a) is a schematic representation of the magnetization curve taken along the length of a conventional resonant marker, where B is the magnetic induction and H is the applied magnetic field;
Fig. 1(b) is a schematic representation of the magnetization curve taken along the length of the marker of the present invention, where Ha is a field above which B saturates;

Fig. 2 is a schematic representation of signal profile detected at the receiving coil depicting mechanical resonance excitation, termination of excitation at time to and subsequent ring-down, wherein V. and V, are the signal amplitudes at the receiving coil at t = to and t = ti (1 msec after to ), respectively;
and Fig. 3 is a schematic representation of the mechanical resonance frequency, fT , and response signal, Vl , detected in the receiving coil at I msec after the termination of the exciting ac field as a function of the bias magnetic field, Hb, wherein Hbl and Hb2 are the bias fields at which Vl is a maximum and fr is a minimum, respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, there are provided magnetic metallic glass alloys that are characterized by relatively linear magnetic responses in the frequency region where harmonic marker systems operate magnetically. Such alloys evidence all the features necessary to meet the requirements of markers for surveillance systems based on magneto-mechanical actuation. Generally stated the glassy metal alloys of the present invention have a composition consisting essentially of the formula Fe, COb Ni. Md Be Sif Cg, where M is selected from molybdenum, chromium and manganese and "a", "b", "c", "d", "e", "f' and "g"
are in atom percent, "a" ranges from about 30 to about 45, "b" ranges from about 4 to about 40 and "c" ranges from about 5 to about 45, "d" ranges from about 0 to about 3, "e" ranges from about 10 to about 25 , "f' ranges from about 0 to about 15 and "g" ranges from about 0 to about 2. The purity of the above compositions is that found in normal commercial practice. Ribbons of these alloys are annealed with a magnetic field applied across the width of the ribbons at elevated temperatures for a given period of time. Ribbon temperatures should be below its crystalization temperature and the ribbon, upon being heat treated, should be ductile enough to be cut up. The field strength during the annealing is such that the ribbons saturate magnetically along the field direction. Annealing time depends on the annealing temperature and typically ranges from about a few minutes to a few hours. For commercial production, a continuous reel-to-reel annealing furace is preferred. In such cases, ribbon travelling speeds may be set at about between 0.5 and about 12 meter per minute. The annealed ribbons having, for example, a length of about 38 mm, exhibit relatively linear magnetic response for magnetic fields of up to 8 Oe or more applied parallel to the marker length direction and mechanical resonance in a range of frequencies from about 48 kHz to about 66 kHz. The linear magnetic response region extending to the level of 8 Oe is sufficient to avoid triggering some of the harmonic marker systems. For more stringent cases, the linear magnetic response region is extended beyond 8 Oe by changing the chemical composition of the alloy of the present invention. The annealed ribbons at lengths shorter or longer than 38 mm evidence higher or lower mechanical resonance frequencies than 48-66 kHz range.
Ribbons having mechanical resonance in the range from about 48 to 66 kHz are preferred. Such ribbons are short enough to be used as disposable marker materials. In addition, the resonance signals of such ribbons are well separated from the audio and commercial radio frequency ranges.
Most metallic glass alloys that are outside of the scope of this invention typically exhibit either non-linear magnetic response regions below 8 Oe level or H.
levels close to the operating magnetic excitation levels of many article detection systems utilizing harmonic markers. Resonant markers composed of these alloys accidentally trigger, and thereby pollute, many article detection systems of the harmonic re-radiance variety.
There are a few metallic glass alloys outside of the scope of this invention that do show linear magnetic response for an acceptable field range. These alloys, however, contain high levels of cobalt or molybdenum or chromium, resulting in increased raw material costs and/or reduced ribbon castability owing to the higher melting temperatures of such constituent elements as molybdenum or chromium.

The alloys of the present invention are advantageous, in that they afford, in combination, extended linear magnetic response, improved mechanical resonance performance, good ribbon castability and economy in production of usable ribbon.
Apart from the avoidance of the interference among different systems, the markers made from the alloys of the present invention generate larger signal amplitudes at the receiving coil than conventional mechanical resonant markers.
This makes it possible to reduce either the size of the marker or increase the detection aisle widths, both of which are desirable features of article surveillance systems.
Examples of inetallic glass alloys of the invention include Fe40 C034 Ni8 B13 Si5 , Fe 40 C030 Ni12 B13 Si5 , Fe40 Co26 Ni 16 B13 Sl 5, Fe 40 Co22 Ni20 B13 Si5 , Fe 40 Co20 Ni22 B13 Si5 , Fe40 Co18 Ni24 B13 Si5 , Fe35 C018 N129 B13 Si5 , Fe32 C018 Ni32 B13 Si5 , Fe40 C016 Ni26 B13 Sls s Fe40 C014 Ni28 B13 Sis , Fe4o C014 Ni28 B16 Si 2, Fe4o C014 Ni28 B11 Si 7, Fe40 C014 N128 B13 Si 3 C 2, Fe 38 CO 14 Ni 30 B 13 Si 5, Fe36 CO 14 Ni 32 B
13 Si 5, Fe34C014N134B 13 S15,Fe30C014Ni38B 13 S15,Fe42C014Ni26B 13 S15, Fe 44 Co 14 Ni 24 B 13 Si 5, Fe4o Co14 Ni27 Mo1 B13 Si5, Fe4o Co14 Ni25 Mo3 B13 Si5, Fe40 Co14 Ni27 Crl B13 Si5, Fe4o Co14 Ni25 Cr3 B13 Si5, Fe40 Co14 Ni25 Mol B13 Si5 C 2, Fe 40 Co 12 Ni 3o B 13 Si 5, Fe 38 CO 12 Ni 32 B 13 Si 5, Fe42 Co 12 Ni 30 B 13 Si 5, Fe40 Co 12 Ni 26 B 17 Si 5, Fe 40 CO 12 Nl 28 B15 Sl 5, Fe40 CO 1o N132 B13 Sl5 , Fe42 CO 10 N130 B13 S15 , Fe44 Co lo Ni28 B13 Si5, Fe4o Co lo Ni31 Mol B13 Si5, Fe4o Co lo Ni31 Crl B13 Si5, Fe4o Co 10 Ni31 Mn1 B13 S15 , Fe40 Co 10 N129 Mn3 B13 S15 , Fe40 Co 10 N130 B13 Si5 C2, Fe4o Co8 Ni38 B13 Si5 , Fe40 C06 Ni36 B13 Si5 , and Fe40 Co4 Ni38 B13 Si5 , wherein subscripts are in atom percent.
The magnetization behavior characterized by a B-H curve is shown in Fig.
1(a) for a conventional mechanical resonant marker, where B is the magnetic induction and H is the applied field. The overall B-H curve is sheared with a non-linear hysteresis loop existent in the low field region. This non-linear feature of the =

marker results in higher harmonics generation, which triggers some of the harmonic marker systems, hence the interference among different article surveillance systems.
The definition of the linear magnetic response is given in Fig. 1(b). As a marker is magnetized along the length direction by an external magnetic field, H, the magnetic induction, B, results in the marker. The magnetic response is relatively linear up to H$ , beyond which the marker saturates magnetically.
The quantity H. depends on the physical dimension of the marker and its magnetic anisotropy field. To prevent the resonant marker from accidentally triggering a surveillance system based on harmonic re-radiance, H. should be above the operating field intensity region of the harmonic marker systems.
The marker material is exposed to a burst of exciting signal of constant amplitude, referred to as the exciting pulse, tuned to the frequency of mechanical resonance of the marker material. The marker material responds to the exciting pulse and generates output signal in the receiving coil following the curve leading to Vo in Fig. 2. At time to , excitation is terminated and the marker starts to ring-down, reflected in the output signal which is reduced from Vo to zero over a period of time. At time tl , which is 1 msec after the termination of excitation, output signal is measured and denoted by the quantity V 1. Thus V I/ V. is a measure of the ring-down. Although the principle of operation of the surveillance system is not dependent on the shape of the waves comprising the exciting pulse, the wave form of this signal is usually sinusoidal. The marker material resonates under this excitation.
The physical principle governing this resonance may be summarized as follows: When a ferromagnetic material is subjected to a magnetizing magnetic field, it experiences a change in length. The fractional change in length, over the original length, of the material is referred to as magnetostriction and denoted by the symbol X. A positive signature is assigned to k if an elongation occurs parallel to the magnetizing magnetic field.

When a ribbon of a material with a positive magnetostriction is subjected to a sinusoidally varying external field, applied along its length, the ribbon will undergo periodic changes in length, i.e., the ribbon will be driven into oscillations.
The external field may be generated, for example, by a solenoid carrying a sinusoidally varying current. When the half-wave length of the oscillating wave of the ribbon matches the length of the ribbon, mechanical resonance results. The resonance frequency fr is given by the relation fT = (1/2L)(E/D)o.s, where L is the ribbon length, E is the Young's modulus of the ribbon, and D is the density of the ribbon.
Magnetostrictive effects are observed in a ferromagnetic material only when the magnetization of the material proceeds through magnetization rotation.
No magnetostriction is observed when the magnetization process is through magnetic domain wall motion. Since the magnetic anisotropy of the marker of the alloy of the present invention is induced by field-annealing to be across the marker width direction, a dc magnetic field, referred to as bias field, applied along the marker length direction improves the efficiency of magneto-mechanical response from the marker material. It is also well understood in the art that a bias field serves to change the effective value for E, the Young's modulus, in a ferromagnetic material so that the mechanical resonance frequency of the material may be modified by a suitable choice of the bias field strength. The schematic representation of Fig. 3 explains the situation further: The resonance frequency, fr, decreases with the bias field, Hb, reaching a minimum, (fr),,,;,,, at H62. The signal response, Vl , detected , say at t = tl at the receiving coil, increases with Hb , reaching a maximum, V. , at Hbl. The slope, dfr /dHb, near the operating bias field is an important quantity, since it related to the sensitivity of the surveillance system.
Summarizing the above, a ribbon of a positively magnetostrictive ferromagnetic material, when exposed to a driving ac magnetic field in the presence of a dc bias field, will oscillate at the frequency of the driving ac field, and when this frequency coincides with the mechanical resonance frequency, fT, of the material, the ribbon will resonate and provide increased response signal amplitudes.
In practice, the bias field is provided by a ferromagnet with higher coercivity than the marker material present in the "marker package".
Table I lists typical values for V. , Hb1, (fr ),,,;,, and Hb2 for a conventional mechanical resonant marker based on glassy Feao Ni38 Moa B18. The low value of Hb2 , in conjunction with the existence of the non-linear B-H bahavior below Hb2, tends to cause a marker based on this alloy to accidentally trigger some of the harmonic marker systems, resulting in interference among article surveillance systems based on mechanical resonance and harmonic re-radiance..
TABLE I
Typical values for V. , Hbl ,(fr ),n;,, and Hb2 for a conventional mechanical resonant marker based on glassy Feao Ni38 Moa B18. This ribbon at a length of 38.1 mm has mechanical resonance frequencies ranging from about 57 and 60 kHz.
mV Hhl-(Oe) (kHz) HbZ (Oe2 Table II lists typical values for Ha, Vm, Hb1, (fr),,,;,, , HbZ and dfr /dHb Hb for the alloys outside the scope of this patent. Field-annealing was performed in a continuous reel-to-reel furnace on 12.7 mm wide ribbon where ribbon speed was from about 0.6 m/min. to about 1.2 m/min.
TABLE II

Values for H,, Vn,, Hbl, H62 and df, /dHb taken at Hb = 6 Oe for the alloys outside the scope of this patent. Field-annealing was performed in a continuous reel-to-reel furnace where ribbon speed was from about 0.6 ni/min.
to about 1.2 m/min with a magnetic field of about 1.4 kOe applied perpendicular to the ribbon length direction.

Comoosition (at%) H. (Oe) y_ (mV) Hpa (00 (G1n:, (kHz) 1i Oe df, fdHe (HzlOo) A C042 Fuo B,3 Sis 22 400 7.0 49.7 15.2 700 B. Co3*Fe4o Ni4B,sSis 20 420 9.3 53.8 16.4 500 C. Co2 Fe.o Ni4o B,3Sis 10 400 3.0 50.2 6.8 2,080 D. Co,oFe.4oNi2-7MnsB,3Sis 7.5 400 2.7 50.5 6.8 2.300 Although alloys A and B show linear magnetic responses for acceptable magnetic field ranges, but contain high levels of cobalt, resulting in increased raw material costs. Alloys C and D have low Hbl values and high dit /dHb values, combination of which are not desirable from the standpoint of resonant marker system operation.

EXAIVIPLES
Example 1: Fe-Co-Ni-B-Si metallic glasses 1. Sample Preparation Glassy metal alloys in the Fe-Co-Ni-B-Si series, designated as samples No.
1 to 29 in Table III and IV, were rapidly quenched from the melt following the techniques taught by Narasimhan in U.S. Patent No. 4,142,571.

All casts were made in an inert gas, using 100 g melts. The resulting ribbons, typically 25 m thick and about 12.7 mm wide, were determined to be free of significant crystallinity by x-ray difi'ractometry using Cu-Ka radiation and differential scanning calorimetry.
Each of the alloys was at least 70 % glassy and, in many instances, the alloys were more than 90 % glassy. Ribbons of these glassy metal alloys were strong, shiny, hard and ductile.
The ribbons were cut into small pieces for magnetization, magnetostriction, Curie and crystallization temperature and density measurements. The ribbons for -magneto-mechanical resonance characterization were cut to a length of about 38.1 mm and were heat treated with a magnetic field applied across the width of the ribbons. The strength of the magnetic field was 1.1 kOe or 1.4 kOe and its direction was varied between 75 and 90 with respect to the ribbon length direction. Some of the ribbons were heat-treated under tension ranging from about zero to 7.2 kg/mmZ applied along the direction of the ribbon. The speed of the ribbon in the reel-to-reel annealing furnace was changed from about 0.5 meter per minute to about 12 meter per minute.

2. Characterization of in etic and thermal properties Table III lists saturation induction (B, ), saturation magnetostriction Q, ), and crystallization (T, ) temperature of the alloys. Magnetization was measured by a vibrating sample magnetometer, giving the saturation magnetization value in emu/g which is converted to the saturation induction using density data.
Saturation magnetostriction was measured by a strain-gauge method, giving in 10~
'25 or in ppm. Curie and crystallization temperatures were measured by an inductance method and a differential scanning calorimetry, respectively.

TABLE ffi Magnetic and thermal properties of Fe-Co-Ni-B-Si glassy alloys. Curie temperatures of alloy No. 22 (6f =447 C), No. 27 (6f =430 C), No. 28 (6f =400 C) and 29 (Af =417 C) could be determined because they are below the first crystallization temperatures (T. ).

No. Composition (at.%) B (Tesla) L" (ppm) Tc ( C) Fe Co Ni B Si 1 40 34 8 13 5 1.46 23 456 2 40 30 12 13 5 1.42 22 455 3 40 26 16 13 5 1.38 22 450 4 40 22 20 13 5 1.32 20 458 5 40 20 22 13 5 1.28 19 452 6 40 18 24 13 5 1.25 20 449 7 35 18 29 13 5 1.17 17 441 8 32 18 32 13 5 1.07 13 435 9 40 16 26 13 5 1.21 18 448 10 40 14 28 13 5 1.22 19 444 11 40 14 28 16 2 1.25 19 441 12 40 14 28 11 7 1.20 15 444 13 38 14 30 13 5 1.19 18 441 14 36 14 32 13 5 1.14 17 437 15 34 14 34 13 5 1.09 17 434 16 30 14 38 13 5 1.00 10 426 17 42 14 26 13 5 1.27 21 448 18 44 14 24 13 5 1.31 21 453 19 40 12 30 13 5 1.20 18 442 20 38 12 32 13 5 1.14 18 440 21 42 12 30 13 3 1.29 21 415 22 40 12 26 17 5 1.12 17 498 23 40 12 28 15 5 1.20 19 480 24 40 10 32 13 5 1.16 17 439 25 42 10 30 13 5 1.15 19 443 26 44 10 28 13 5 1.25 20 446 27 40 8 34 13 5 1.11 17 437 28 40 6 36 13 5 1.12 17 433 29 40 4 38 13 5 1.09 17 430 Each marker material having a dimension of about 38.1mnix12.7mmx20 m was tested by a conventional B-H loop tracer to measure the quantity of H. and then was placed in a sensing coil with 221 turns. An ac magnetic field was applied along the longitudinal direction of each alloy marker with a dc bias field changing from 0 to about 20 Oe. The sensing coil detected the magneto-mechanical response of the alloy marker to the ac excitation. These marker materials mechanically resonate between about 48 and 66 kHz. The quantities characterizing the magneto-mechanical response were measured and are listed in Table IV for the alloys listed in Table III.

TABLE IV

Values of H. , V. , Hbi (f r),r,;,, , Hb2 and dfr /dHb taken at Hb = 6 Oe for the alloys of Table III heat-treated at 380 C in a continuous reel-to-reel furnace with a ribbon steed of about 1.2 m/minute and at 415 C for 30 min (indicated by asterisks *). The annealing field was about 1.4 kOe applied perpendicular to the ribbon length direction.
Allov No. H, (Oe) V m Hbi Oe L~, (kHzl H, Oe df /dH,, (Hz/Oe) 1 21 415 10.3 54.2 16.5 460 2 20 370 10.7 54.2 16.0 560 3 20 370 10.0 53.8 16.5 430 4* 20 250 10.5 49.8 17.7 450 4 18 330 8.0 53.6 14.2 590 5 17 270 9.0 52.0 14.5 710 6 17 340 7.8 53.4 14.2 620 7 16 300 8.6 53.5 14.3 550 8 15 380 8.0 54.1 13.0 580 9 16 450 7.8 51.3 14.2 880 10* 17 390 8.9 49.3 15.9 550 16 390 7.0 52.3 13.4 810 11 15 350 8.0 52.3 13.9 750 5 12 14 350 7.0 52.5 12.4 830 13 14 400 7.3 52.5 13.1 780 =
14 13 330 6.5 54.2 12.6 670 13 270 6.2 53.0 11.5 820 16 10 230 5.0 56.0 9.3 1430 10 17 15 415 7.2 51.2 14.3 740 18 15 350 7.7 50.4 12.9 1080 19 14 440 6.5 50.6 11.6 960 14 330 6.6 52.9 11.3 900 21 19_ 325 9.3 53.9 14.8 490 15 22 9 260 3.5 55.8 8.0 1700 23 11 310 5.4 52.2 10.5 1380 24* 15 220 8.2 48.5 13.7 740 24 14 410 7.5 51.8 13.5 800 13 420 6.2 49.5 12.2 1270 20 26 14 400 6.0 50.2 12.8 1050 27 10 250 4.0 51.9 8.5 1490 28 12 440 4.0 49.7 9.0 1790 29 11 380 5.2_ 51.5 9.8 1220 All the alloys listed in Table IV exhibit H. values exceeding 8 Oe, which make them possible to avoid the interference problem mentioned above. Good sensitivity ( df, /dHb ) and large response signal ( Vm ) result in smaller markers for resonant marker systems.
The quantities characterizing the magneto-mechanical resonance of the marker material of Table III heat-treated under different annealing conditions are summarized in Tables V, VI, VII, VIII and IX.

TABLE V
Values of V. , Hb1 ,(fr)n,iõ , dfr /dHb taken at Hb = 6 Oe for alloy No. 8 of Table III heat-treated under different conditions in a reel-to-reel annealing furnace.
Applied field direction indicated is the angle btween the ribbon length direction and -the field direction.

Annealing Temperature: 440 C Applied Field/Direction: 1.1 kOe / 90 Hb~2 df / dFib Ribbon Speed Tension V H tL)~.
(m/minute) (kg/mm2) (mV) (Oe) (kHz) (Oe) (Hz/Oe) 9.0 1.4 360 3.9 55.3 8.5 590 10.5 1.4 340 3.8 55.4 8.5 540 10.5 6.0 225 5.0 55.8 9.8 690 1= t 1'_a.' t l 1_/l_ /!lA
-on .
~: 1. 1 Kve t 7v Anneaiing l~emperature:-400O - C. Appued FieiaiTLire_ cLi -Ribbon Speed Tension V H ~f )m Hh d-rf / dHb (m/minute) (kg/mmZ) (mV) (Oe) (kHz) (Oe) (Hz/Oe) 9.0 0 300 4.1 53.7 8.3 1170 9.0 7.2 250 5.2 55.9 9.7 AnnealingTemperature: 340 C Applied Field Direction: 1.1 kOe / 75 Ribbon Speed Tension V H (f~ Hb= df / dHb (m/minute) (kg/mrnz) (mV) (Oe) (kHz) (Oe) (Hz/Oe) 0.6 0 315 7.9 55.7 13.4 420 2.1 0 225 8.0 56.1 12.8 470 TABLE VI

Values of V. , Hbl ,(Qn,;,, , df, /dHb taken at Hb = 6 Oe for alloy No. 17 of Table III heat-treated under different conditions in a reel-to-reel annealing furnace.
Applied field direction indicated is the angle btween the ribbon length direction and the field direction.
Annealing Temperature: 320 C Applied Field/Direction: 1.4 kOe / 90 Ribbon Speed Tension Vm H fLL1,,,,,, x, , d / dHb (m/minute) (kg/mmZ) (mV) (Oe) (kHz) (Oe) (Hz/Oe) 0.6 0 250 6.0 55.3 13.0 670 0.6 1.4 320 6.0 54.0 14.1 620 0.6 3.6 370 7.0 52.2 14.0 630 Annealing Temperature: 280 C Applied Field/Direction: 1.1 kOe / 90 Ribbon Sueed Tension V H (f L1m;" Hh? drf dH
(m/minute) (kg/mm2) (mV) (Oe) (kHz) (Oe) (HzJOe) 0.6 7.2 390 7.0 53.2 13.9 615 2.1 7.2 240 5.0 53.6 11.5 760 Annealin,g Temperature: 280 C Applied Field/Direction: 1.1 kOe / 75 Ribbon Speed Tension V4. H (f ~ H,, df dHb (m/minute) (kg/mm2) (mV) (Oe) (kHz) (Oe) (HzJOe) 0.6 7.2 360 6.3 52.9 13.2 630 2.1 7.2 270 5.2 53.2 11.2 860 TABLE VII

Values of V. , Hbl ,(f,),,,;,, , df, /dHb taken at Hb = 6 Oe for alloy No. 24 of Table III heat-treated under different conditions in a reel-to-reel annealing furnace.
Applied field direction indicated is the angle btween the ribbon length direction and the field direction.
Annealing Temperature: 320 C Applied Field/Direction: 1.1 kOe / 90 Ribbon Speed Tension V H (f jm,,, H~, f / Hh (m/minute) (kg/mm2) (mV) (Oe) (kHz) (Oe) (Hz/Oe) 0.6 0 280 8.0 54.7 13.1 450 2.1 0 310 7.6 54.7 12.0 500 2.1 7.2 275 8.0 55.1 14.5 450 Annealing Temperature: 320 C Aonlied Field/Direction: 1.1 kOe / 75 Ribbon Speed Tension V Hm ff r 1m;" HbZ d,f / dH
(m/minute) (kg/mm2) (mV) (Oe) (kHz) (Oe) (Hz/Oe) 0.6 0 310 8.2 54.7 13.0 530 0.6 7.2 275 8.2 55.2 15.0 430 2.1 0 290 7.2 54.8 12.0 550 2.1 7.2 270 7.0 55.6 13.5 480 Annealing Temperature: 300 C Applied Field/Direction: 1.1 kOe / 82.5 Ribbon Speed Tension Vm Hm If m HbQ df / dHb (m/minute) (kg/mm') (mV) (Oe) (kHz) (Oe) (Hz/Oe) 0.6 2.1 300 8.3 54.9 13.7 410 2.1 2.1 300 7.0 54.4 11.8 480 AnnealingTemperature: 280 C Applied Field/Direction: 1.1 kOe / 90 Ribbon Speed Tension V H LL)= Hu df, / dHb (m/minute) (kg/mm') (mV) (Oe) (kHz) (Oe) (Hz/Oe) 0.6 0 265 8.4 55.2 12.6 430 2.1 7.2 255 6.8 55.9 12.0 490 TABLE VIII
Values of Vm , Hbi ,(fr)n,;n , df, /dHb taken at Hb = 6 Oe for alloy No. 27 of Table III heat-treated under different conditions in a reel-to-reel annealing furnace.
Applied field direction indicated is the angle btween the ribbon length direction and the field direction.

Annealing Temperature: 300 C Applied Field/Direction: 1.1 kOe / 82.5 Ribbon Sueed Tension Vm H f(lm , H, f dHh (m/minute) (kg/mm2) (mV) (Oe) (kHz) (Oe) (HWOe) 0.6 2.1 270 6.2 53.8 11.9 690 2.1 2.1 270 5.2 52.9 10.5 870 Annealina Temperature: 280 C Applied Field/Direction: 1.1 kOe / 90 Ribbon Sueed Tension V H (f ? .. H Z df, / dHb (m/minute) (kg/mm2) (mV) (Oe) (kHz) (Oe) (Hz/Oe) 0.6 7.2 290 5.8 53.8 12.0 670 2.1 0 230 6.0 54.3 11.0 720 TABLE IX

-Values of V,,, , Hb, ,(Q,,,iõ , dfr /dHb taken at Hb = 6 Oe for alloy No. 29 of Table III heat-treated under different conditions in a reel-to-reel annealing furnace.
Applied field direction indicated is the angle btween the ribbon length direction and the field direction.
Annealiniz Temperature: 320 C Applied Field/Direction: 1.1 kOe / 90 Ribbon Speed Tension V H !f E~ Hb, df, / dH
(m/minute) (kg/mm2) (mV) (Oe) (kHz) (Oe) (Hz/oe) 2.1 7.2 225 4.7 55.2 10.0 570 Annealing Temperature: 280 0 C Applied Field/Direction: 1.1 kOe / 75 Ribbon Speed Tension V H ff,)= H2 df / dHb (m/minute) (kg/mmZ) (mV) (Oe) (kHz) (Oe) (HzJOe) 0.6 0 230 5.8 54.2 11.0 720 0.6 7.2 245 5.2 54.7 11.2 620 Above tables indicate that desired performance of a magneto-mechanical resonant marker can be achieved by proper combination of alloy chemistry and heat-treatment conditions.

Example 2: Fe-Co-Ni-Mo/Cr/Mn-B-Si-C metallic glasses Glassy metal alloys in the Fe-Co-Ni-Mo/Cr/Mn-B-Si-C system were prepared and characterized as detailed under Example 1. Table X lists chemical compositions, magnetic and thermal properties and Table XI lists quantities characterizing mechanical resonance responses of the alloys of Table X.

WO 96/32518 PCT/1.TS96/05093 TABLE X

Magnetic and thermal properties of low cobalt containing glassy alloys. T.
is the first crystallization temperature.

Alloy No. Composition (at.%) B L
Fe Co Ni Mo Cr Mn B Si C (Tesla) (ppm) ( C) 1 40 14 28 - - - 13 3 2 1.22 19 441 2 40 14 27 1 - - 13 5 1.18 18 451 3 40 14 25 3 - 13 5 - 1.07 13 462 4 40 14 27 - 1 - 13 5 1.18 20 462 5 40 14 25 - 3 - 13 5 1.07 15 451 6 40 14 25 1 - - 13 5 2 1.15 15 480 7 40 10 31 1 - - 13 5 - 1.12 18 447 8 40 10 31 - 1 - 13 5 - 1.13 18 441 9 40 10 31 - - 1 13 5 - 1.16 18 445 10 40 10 29 - - 3 13 5 - 1.19 17 454 11 40 10 30 - - - 13 5 2 1.13 16 465 TABLE XI

Values of Ha , V. , Hbl ,( fr ),,,;,, , Hb2 and dfr /dHb taken at Hb = 6 Oe for the alloys listed in Table X heat-treated at 380 C in a continuous reel-to-reel furnace with a ribbon speed of about 0.6 m/minute with a field of 1.4 kOe applied across the ribbon width.

Allov No. H. (Oe) V ,,CmN/j H,(Oe) (f~kHz Hhy fOe1 df /dHb (Hz/Oe1 1 14 310 8.3 52.5 13.1 870 2 13 350 4.4 51.7 10.0 1640 3 12 250 3.0 51.7 6,4 1790 4 11 320 6.2 51.8 9.8 950 10 480 3.7 51.5 8.2 1780 5 6 9 390 4.1 52.0 8.5 1820 7 10 460 4.2 50.3 8.9 1730 8 10 480 5.2 51.6 9.8 1560 9 12 250 6.5 51.2 10.6 1000 10 380 3.5 51.0 7.8 1880 10 11 9 310 4.0 51.5 8.0 1880 All the alloys listed in Table XI exhibit H. values exceeding 8 Oe, which make them possible to avoid the interference problems mentioned above. Good sensitivity ( dfr /dHb ) and large magneto-mechanical resonance response signal ( Vm ) result in smaller markers for resonant marker systems.
Having thus described the invention in rather full detail, it will be understood that such detail need not be strictly adhered to but that further changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the subjoined claims.

Claims (24)

What is claimed is:

1. A magnetic metallic glass alloy that is at least about 70% glassy, has been annealed to enhance magnetic properties, and has a composition consisting essentially of the formula Fe a CO b Ni c M d B e Si f C g where M is at least one member selected from the group consisting of molybdenum, chromium and manganese, "a", "b", "c", "d", "e", "f" and "g" are in atom percent, "a" ranges from about 30 to about 45, "b" ranges from about 4 to about 40 and "c" ranges from about 5 to about 45, "d" ranges from about 0 to about 3, "e" ranges from about 10 to about 25 ,"f' ranges from about 0 to about 15 and "g" ranges from about 0 to about 2, said alloy having the form of a heat-treated strip that exhibits mechanical resonance in a range of frequencies from about 48 kHz to about 66 kHz, and having a relatively linear magnetization behavior up to a minimum bias field of about 8 Oe.

2. An alloy as recited by claim 1, wherein the slope of the mechanical resonance frequency versus bias field at about 6 Oe is close to or exceeds about 400 Hz/Oe.

3. An alloy as recited by claim 1 or 2, wherein the bias field at which the mechanical resonance frequency takes a minimum is close to or exceeds about 8 Oe.

4. An alloy as recited by claim 1, wherein M is molybdenum.

5. An alloy as recited by claim 1, wherein M is chromium.

6. An alloy as recited by claim 1, wherein M is manganese.

7. An alloy as recited by ane of of claims I to 6, wherein "a" ranges from about 30 to about 45, the sum of "b" plus "c" ranges from about 32 to about 47, and the sum of "e" plus "f' plus "g" ranges from about 16 to about 22.

8. A magnetic alloy as recited by claim 7, having a composition selected from the group consisting ofFe40 Co34 Nig B13 Si5, Fe 40 Co30 Ni12 B13 Si5 , Fe40 Co26 Ni 16 B13 Si 5, Fe 40 Co22 Ni20 B13 Si5, Fe 40 CO20 Ni22 B13 Si5, Fe40 Co18 Ni24 B13 Si5 , Fe35 C018 Ni29 B13 Si5 , Fe32 Co18 Ni32 B13 Si5 , Fe40 Co16 Ni26B13 Si5, Fe40 Co14 Ni2g B13 Si5, Fe40 Co14 Ni28 B16 Si 2, Fe40 Co14 Ni24 B11 Si 7, Fe40 Co14 Ni28 B13 Si 3 C 2, Fe 38 CO 14 Ni 30 B 13 Si 5, Fe36 CO 14 Ni 32 B 13 Si 5, Fe 34 C014 Ni 34 B 13 Si 5, Fe 30 CO14 Ni 38 B 13 Si 5, Fe42Co 14Ni26B 13Si5,Fe44Co 14Ni24B 13Si5,Fe40Co14Ni27Mo1B13 Si5, Fe40 Co14 Ni25 M03 B13 S15 , Fe40 Co14 Ni27 Cr1 B13 S15 , Fe40 CO14 Ni25 Cr3 B13 Si5, Fe40 Co14 Ni25 Mo1 B13 Si5 C 2, Fe 40 Co 12 Ni 3o B 13 Si5, Fe38CO 12Ni32B 13 Si5,Fe42Co12Ni30B 13Si5,Fe40Co 12 Ni 26 B 17Si5, Fe40 Co 12 Ni32B15Si 5, Fe40 Co 10Ni32 B13Si5, Fe42 Co 10Ni30 B13 Si5 , Fe44 Co 10 Ni28 B 13 Si5 , Fe40 CO 10 Ni31 MO1 B 13Si5, Fe40 Co 10 Ni31 Cr1 B
13 Si5 , Fe40 Co 10 Ni31 Mn1 B13 Si5, Fe40 Co 10 Ni29 Mn3 B13 Si5 , Fe40 Co 10 Ni30 B13 Si5 C2, Fe40 Co g N38 B13Si5, Fe40 Co6 Ni36 B13 Si5, and Fe40 Co4 Ni38 B13 Si5 , wherein subscripts are in atom percent.

9. In an article surveillance system adapted to detect a signal produced by mechanical resonance of a marker within an applied magnetic field, the improvement wherein said marker comprises at least one strip of ferromagnetic material that is at least about 70 % glassy, has been annealed to enhance magnetic properties and has a composition conSi5ting essentially of the formula Fe, Co b Ni, M d B e Si f C g, where M at least one member selected from the group consisting of molybdenum, chromium and manganese, "a", "b", "c", "d", "e", "f' and "g" are in atom percent, "a" ranges from about 30 to about 45, "b" ranges from about 4 to about 40, "c" ranges from about 5 to about 45, "d" ranges from about 0 to about 3, "e" ranges from about 10 to about 25, "f' ranges from about 0 to about 15 and "g" ranges from about 0 to about 2, wherein said strip exhibits mechanical resonance in a range of frequencies from about 48 kHz to about 66 kHz, and a relatively linear magnetization behavior up to a bias field of at least 8 Oe.

10. An article surveillance system as recited by claim 9, wherein said strip is selected from the group consisting of ribbon, wire and sheet.

11. An article surveillance system as recited by claim io, wherein said strip is a ribbon.

12. An article surveillance system as recited by ane one of claims 9 to 11, wherein the slope of the mechanical resonance frequency versus bias field for said strip at about 6 Oe is close to or exceeds about 400 Hz/Oe.

13. An article surveillance system as recited by any one of claims 9 to 12, wherein the bias field at which the mechanical resonance frequency of said strip takes a minimum is close to or exceeds about 8 Oe.

14. An article surveillance system as recited by claim 9, wherein M is molybdenum.

15. An article surveillance system as recited by claim 9, wherein M is the element chromium.

16. An article surveillance system as recited by claim 9, wherein M is the element manganese.

17. An article surveillance system as recited by any one of claims 9 to 16, wherein "a"
ranges from about 30 to about 45, the sum of "b" plus "c" ranges from about 32 to about 47, and the sum of "e" plus "f' plus "g" ranges from about 16 to about 22.

18. An article surveillance system as recited by claim 9, wherein said strip has a composition selected from the group consisting of Fe40 Co34 Nig B13 Si5, Fe 40 Co30 Ni12 B13 Si5 , Fe40 Co26 Ni 16 B13 Si5, Fe 40 Co22 Ni20 B13 Si5, Fe 40 Co20 Ni22 B13 Si5 , Fe40 Co18 Ni24 B13 Si5, Fe35 Co18 Ni29 B13 Si5, Fe32 Co18 Ni32 B13 Si5 , Fe40 Co16 Ni26 B13 Si5,Fe40 Co14 Ni2g B13 Si5 , Fe40 Co14 Ni2g B16 Si 2, Fe40 Co14 Ni28 B11 Si 7, Fe40 Co14 Ni28 B13 Si 3 C 2, Fe38Co14Ni30B 13 Si5,Fe36Co14Ni32B 13Si5,Fe34Co14Ni34B 13Si5, Fe30Co14Ni38 B13Si5,Fe42Co14Ni26B13Si5,Fe44Co14Ni24B13Si5, Fe40 Co14 Ni27 Mo1 B13 Si5, Fe40 Co14 Ni25 Mo3 B13 Si5 , Fe40 Co14 Ni27 Cr1 B13 Si5 , Fe40 Co14 Ni25 Cr3 B13 Si5 , Fe40 Co14 Ni25 Mo1 B13 Si5 C 2, Fe 40 Co 12 Ni 30 B 13 Si5, Fe38Co12Ni32B13Si5,Fe42Co 12Ni30B13Si5,Fe40Co12Ni26B17 Si5, Fe40 Co 12 Ni 28 B15 Si5, Fe40 Co 10 Ni32 B13 Si5 , Fe42 Co 10 Ni3o B13 Si5 , Fe44 Co 10 Ni2g B13 Si5, Fe40 Co 10 Ni31 Mo1 B13 Si5, Fe40 Co 10 Ni31 Cr1 B13 Si5 , Fe40 Co 10 Ni31 Mn1 B13 Si5 , Fe40 Co 10 Ni29 Mn3 B13 Si5 , Fe40 Co 10 Ni30 B13 Si5 C2, Fe40 CO g Ni38 B13 Si5, Fe40 Co6 Ni36 B13 Si5 , and Fe40 Co 4 Ni38 B13 Si5 , wherein subscripts are in atom percent.

19. An alloy as recited by any one of claims 1 to 8, wherein the anneal is in a magnetic field.

20. An alloy as recited in claim 19, wherein said magnetic field is applied at a field strength such that said strip saturates magnetically along the field direction.

21. An alloy as recited in claim 20, wherein said strip has a length direction and said magnetic field is applied across siad strip width direction, the direction of said magnetic field ranging from about 75 ° to about 90 ° with respect to the strip length direction.

22. An alloy as recited by claim 21, wherein said magnetic field has a magnitude ranging from about 1 to about 1.5 kOe.

23. An alloy as recited by claim 21, wherein said heat-treatment step is carried out for a time period ranging from a few minues to a few hours at a temperature below the alloy's crystallization temperature.

24. An alloy recited by claim 1, wherein said heat-treatment is carried out in a continuous reel-to-reel furnace, said magnetic field has a magnitude ranging from about 1 to 1.5 kOe applied across said strip width rection making an angle ranging from about 75 ° to about 90 ° with respect to said strip length direction and said strip has a width ranging from about one millimeter to about 15 mm and a speed ranging from about 0.5 m/min. to about 12 m/min. and is under a tension ranging from about zero to about 7.2 kg/mm2, the temperature of said heat-treatment being determined such that the temperature of said strip is below its crystallization temperature and said strip, upon being heat-treated, is ductile enough to be cut.