EP2277180A1

EP2277180A1 - Method for producing metal-based materials for magnetic cooling or heat pumps

Info

Publication number: EP2277180A1
Application number: EP09738093A
Authority: EP
Inventors: Ekkehard BRÜCK; Thanh Trung Nguyen
Original assignee: Technology Foundation - STW; Stichting voor de Technische Wetenschappen STW; Universiteit Van Amsterdam
Current assignee: Technology Foundation - STW; Stichting voor de Technische Wetenschappen STW; Universiteit Van Amsterdam
Priority date: 2008-04-28
Filing date: 2009-04-27
Publication date: 2011-01-26
Anticipated expiration: 2029-04-27
Also published as: CA2721621A1; NZ588756A; JP2011523676A; CN102017025A; AU2009242216A1; EP2277180B1; AU2009242216B2; WO2009133049A1; TW201009855A; US20110061775A1; JP5855457B2; BRPI0911771A2; CN102017025B; TWI459409B; KR101553091B1; AU2009242216C1; KR20110036700A; AU2014203376A1

Abstract

The method for producing metal-based materials for magnetic cooling or heat pumps comprises the following steps: a) reacting chemical elements and/or alloys in a stoichiometry which corresponds to the metal-based material in the solid and/or liquid phase, b) optionally converting the reaction product from step a) into a solid, c) sintering and/or tempering the solid from step a) or b), d) quenching the sintered and/or tempered solid from step c) at a cooling speed of at least 100 K/s.

Description

Process for the production of metal-based materials for magnetic cooling or heat pumps

description

The invention relates to processes for the production of metal-based materials for magnetic cooling or heat pumps, such materials and their use. The materials produced according to the invention are used in magnetic cooling, in heat pumps or air conditioning systems.

Such materials are known in principle and described for example in WO 2004/068512. The magnetic cooling techniques are based on the magnetocaloric effect (MCE) and may be an alternative to the known steam-cycle cooling methods. In a material exhibiting a magnetocaloric effect, the alignment of randomly oriented magnetic moments with an external magnetic field results in heating of the material. This heat can be dissipated by the MCE material into the ambient atmosphere through a heat transfer. When the magnetic field is then turned off or removed, the magnetic moments revert to a random arrangement, causing the material to cool to below ambient temperature. This effect can be exploited for cooling purposes, see also Nature, Vol. 415, 10 January 2002, pages 150 to 152. Typically, a heat transfer medium such as water is used for heat removal from the magnetocaloric material.

The preparation of conventional materials is carried out by solid phase reaction of the starting materials or starting alloys for the material in a ball mill, subsequent compression, sintering and annealing under an inert gas atmosphere and subsequent slow cooling to room temperature. Such a method is described, for example, in J. Appl. Phys. 99, 2006, 08Q107.

Processing by melt spinning is also possible. As a result, a more homogeneous element distribution is possible, which leads to an improved magnetocaloric effect, see Rare Metals, Vol. 25, October 2006, pages 544-549. In the process described therein, the starting elements are first induction-melted in an argon gas atmosphere and then sprayed in the molten state via a nozzle onto a rotating copper roller. This is followed by sintering at 1000 ^° C. and slow cooling to room temperature.

The materials obtained by the known method often show a large thermal hysteresis. For example, in compounds of the Fe ₂ P type, those with Germanium or silicon are substituted, large values for thermal hysteresis are observed in a wide range of 10 K or more. Thus, these materials are less suitable for magnetocaloric cooling.

The object of the present invention is to provide a method for producing metal-based materials for magnetic cooling, which leads to a reduction of the thermal hysteresis. At the same time, preferably a large magnetocaloric effect (MCE) should be achieved.

The object is achieved by a method for producing metal-based materials for magnetic cooling or heat pumps, comprising the following steps

a) conversion of chemical elements and / or alloys in a stoichiometry corresponding to the metal-based material, in the solid and / or liquid phase,

b) optionally converting the reaction product from stage a) into a solid,

c) sintering and / or annealing the solid from step a) or b),

d) quenching the sintered and / or tempered solid from step c) with a cooling rate of at least 100 K / s.

It has been found according to the invention that the thermal hysteresis can be significantly reduced if the metal-based materials are not slowly cooled to ambient temperature after sintering and / or annealing, but are quenched at a high cooling rate. The cooling rate is at least 100 K / s. The cooling rate is preferably 100 to 10,000 K / s, more preferably 200 to 1300 K / s. Especially preferred are cooling rates of 300 to 1000 K / s.

Quenching can be achieved by any suitable cooling method, for example by quenching the solid with water or aqueous liquids, for example, cooled water or ice / water mixtures. The solids can be dropped, for example, in iced water. It is also possible to quench the solids with undercooled gases such as liquid nitrogen. Other quenching methods are known to those skilled in the art. The advantage here is a controlled and rapid cooling. Without being bound by theory, the reduced hysteresis can be attributed to smaller grain sizes for the quenched (quenched) compositions.

In the previously known methods, the sintering and tempering were slowly cooled, which leads to the formation of larger particle sizes and thus to the enhancement of the thermal hysteresis.

The rest of the preparation of the metal-based materials is less critical, as long as the quenching of the sintered and / or tempered solid takes place in the last step with the cooling rate of the invention. The method can be applied to the production of any suitable metal-based materials for magnetic cooling. Typical materials for the magnetic cooling are multimetal materials which often contain at least three metallic elements and optionally also non-metallic elements. The term "metal-based materials" indicates that the majority of these materials is composed of metals or metallic elements, typically the proportion of the total material is at least 50% by weight, preferably at least 75% by weight, in particular at least 80% by weight Suitable metal-based materials are explained in more detail below.

In step (a) of the method according to the invention, the reaction of the elements and / or alloys contained in the later metal-based material takes place in a stoichiometry corresponding to the metal-based material in the solid or liquid phase.

Preferably, the reaction in step a) is carried out by heating the elements and / or alloys together in a closed container or in an extruder, or by solid-phase reaction in a ball mill. Particularly preferably, a solid phase reaction is carried out, which takes place in particular in a ball mill. Such an implementation is known in principle, compare the introductory listed writings. In this case, powders of the individual elements or powders of alloys of two or more of the individual elements, which are present in the later metal-based material, are typically powder-mixed in suitable proportions by weight. If necessary, additional grinding of the mixture can be carried out to obtain a microcrystalline powder mixture. This powder mixture is preferably heated in a ball mill, which leads to a further reduction as well as good mixing and to a solid phase reaction in the powder mixture. Alternatively, the individual elements are mixed in the selected stoichiometry as a powder and then melted.

The common heating in a closed container allows the fixation of volatile elements and the control of the stoichiometry. Especially with the use of phosphorus, this would easily evaporate in an open system.

The reaction is followed by sintering and / or tempering of the solid, wherein one or more intermediate steps may be provided. For example, the solid obtained in step a) can be pressed before it is sintered and / or tempered. As a result, the density of the material is increased, so that there is a high density of the magnetocaloric material in the subsequent application. This is particularly advantageous because the volume in which the magnetic field prevails can be reduced, which can be associated with significant cost savings. The pressing is known per se and can be carried out with or without pressing aids. In this case, any suitable shape can be used for pressing. By pressing, it is already possible to produce shaped bodies in the desired three-dimensional structure. The pressing may be followed by sintering and / or tempering step c) followed by quenching step d).

Alternatively, it is possible to feed the solid obtained from the ball mill to a melt spinning process. Melt spinning processes are known per se and described for example in Rare Metals, Vol. 25, October 2006, pages 544 to 549 as well as in WO 2004/068512.

In this case, the composition obtained in step a) is melted and sprayed onto a rotating cold metal roller. This spraying can be achieved by means of positive pressure in front of the spray nozzle or negative pressure behind the spray nozzle. Typically, a rotating copper drum or roller is used which, if desired, may be cooled. The copper drum preferably rotates at a surface speed of 10 to 40 m / s, in particular 20 to 30 m / s. On the copper drum, the liquid composition is cooled at a rate of preferably 10 ² to 10 ⁷ K / s, more preferably at a rate of at least 10 ⁴ K / s, in particular at a rate of 0.5 to 2 x 10 ⁶ K / s.

The melt spinning can be carried out as well as the reaction in step a) under reduced pressure or under an inert gas atmosphere. The Meltspinning a high processing speed is achieved because the subsequent sintering and annealing can be shortened. Especially on an industrial scale, the production of metal-based materials becomes much more economical. Spray drying also leads to a high processing speed. Particular preference is given to melt spinning (middle spinning).

Alternatively, in step b), a spray cooling may be carried out, in which a melt of the composition from step a) is sprayed into a spray tower. The spray tower can be additionally cooled, for example. In spray towers cooling rates in the range of 10 ³ to 10 ⁵ K / s, in particular about 10 ⁴ K / s are often achieved.

The sintering and / or tempering of the solid takes place in stage c) preferably first at a temperature in the range from 800 to 1400 ^° C. for sintering and subsequently at a temperature in the range from 500 to 750 ^° C. for tempering. These values apply in particular to shaped bodies, while for powders lower sintering and tempering temperatures can be used. For example, then the sintering at a temperature in the range of 500 to 800 ⁰ C take place. For Formkör- per / solid state sintering is particularly preferably at a temperature in the range 1000 to 1300 ⁰ C, in particular from 1100 to 1300 ⁰ C. The heat can then be effected for example with 600 to 700 ^0C.

The sintering is preferably carried out for a period of 1 to 50 hours, more preferably 2 to 20 hours, especially 5 to 15 hours. The annealing is preferably carried out for a time in the range of 10 to 100 hours, particularly preferably 10 to 60 hours, in particular 30 to 50 hours. Depending on the material, the exact time periods can be adapted to the practical requirements.

When using the melt spinning method, sintering can often be dispensed with, and tempering can be greatly shortened, for example, for periods of 5 minutes to 5 hours, preferably 10 minutes to 1 hour. Compared to the usual values of 10 hours for sintering and 50 hours for tempering, this results in an extreme time advantage.

The sintering / tempering causes the grain boundaries to melt, so that the material continues to densify. By melting and rapid cooling in stage b), the time duration for stage c) can thus be considerably reduced. This also allows for continuous production of the metal-based materials.

Particularly preferred according to the invention is the process sequence

a) Solid phase conversion of chemical elements and / or alloys in a stoichiometry, which corresponds to the metal-based material, in a ball mill,

b) melt spinning the material obtained in step a),

c) annealing the solid from step b) for a period of 10 seconds or 1 minute to 5 hours, preferably 30 minutes to 2 hours at a temperature in the range of 430 to 1200, preferably 800 to 1000 ⁰ C.

d) quenching the tempered solid from step c) with a cooling rate of 200 to 1300 K / s.

The method of the invention can be used for any suitable metal-based materials.

Particularly preferably, the metal-based material is selected from

(1) Compounds of the general formula (I)

(A _y B _y-1 ) _{2 + δ} C _w D _x E _z (I) meaning

A Mn or Co,

B Fe, Cr or Ni,

C, D, E at least two of C, D, E are different from each other, have a non-vanishing concentration and are selected from P,

B, Se, Ge, Ga, Si, Sn, N, As and Sb, wherein at least one of C, D and E is Ge or Si,

δ number in the range of -0.1 to 0.1 w, x, y, z are numbers in the range of 0 to 1, where w + x + z = 1;

(2) La and Fe based compounds of the general formulas (II) and / or (III) and / or (IV)

La (Fe _x Al _1-X ) ₁₃ H _y or La (Fe _x Si _1-x ) ₁₃ H _y (II)

with x number from 0.7 to 0.95

y is from 0 to 3, preferably from 0 to 2;

La (Fe _x Al y CO _z ) ₁₃ or La (Fe _x Si _y Co _z ) ₁₃ (III)

With

x number from 0.7 to 0.95

y number from 0.05 to 1 - x

z number from 0.005 to 0.5;

LaMn _x Fe ₂ - _x Ge (IV)

With

x number from 1, 7 to 1, 95 and

(3) Heusler alloys of the type MnTP with T transition metal and P a p-doping metal with an electron count per atom e / a in the range of 7 to

8.5.

Particularly suitable materials according to the invention are described, for example, in WO 2004/068512, Rare Metals, Vol. 25, 2006, pages 544 to 549, J. Appl. Phys. 99, 08Q107 (2006), Nature, Vol. 415, January 10, 2002, pages 150 to 152 and Physica B 327 (2003), pages 431 to 437.

In the aforementioned compounds of the general formula (I), C, D and E are preferably identical or different and selected from at least one of P, Ge, Si, Sn and Ga. The metal-based material of the general formula (I) is preferably selected from at least quaternary compounds which in addition to Mn, Fe, P and optionally Sb also Ge or Si or As or Ge and Si or Ge and As or Si and As or Ge, Si and As included.

At least 90% by weight, more preferably at least 95% by weight, of component A are Mn. At least 90% by weight, more preferably at least 95% by weight, of B Fe are preferred. Preferably, at least 90 wt .-%, more preferably at least 95 wt .-% of C P. Preferred are at least 90 wt .-%, more preferably at least 95 wt .-% of D Ge. At least 90% by weight, more preferably at least 95% by weight, of E Si are preferred.

Preferably, the material has the general formula MnFe (P _w Ge _x Si _z ).

Preferably, x is a number in the range of 0.3 to 0.7, w is less than or equal to 1-x and z corresponds to 1-x-w.

The material preferably has the crystalline hexagonal Fe ₂ P structure. Examples of suitable structures are MnFePo, 45 to o, 7, Ge _o, ₅ up to 5 0.30 and MnFeP _0, ₅ to 0.70, (Si / Ge) _0, ₅ to

0,30-

Suitable compounds are also M _n n- _x Fe ₁ . _x P ₁ . _y Ge _y with x in the range of -0.3 to 0.5, y in the range of 0.1 to 0.6. Also suitable are compounds of the general formula Mni ₊ χFei.χPi.yGe _y . _z Sb _z with x in the range of -0.3 to 0.5, y in the range of 0.1 to 0.6 and z smaller than y and smaller than 0.2. Furthermore, compounds of the formula Mnn-xFei-χPi _y Ge _y - _z Si _{z are} suitable with x number in the range of 0.3 to 0.5, y in the range of 0.1 to 0.66, z less than or equal to y and less than 0.6.

Preferred La and Fe-based compounds of the general formulas (II) and / or (III) and / or (IV) are La (Fe _o, _9O Si _Oi i _O) i _3, La (Fe ₀₁ SgSiO ₁ Ii) Is, La (Fe ₀₁ Ss ₀ Si ₀₁ I ₂₀ ) Is, La (Fe _θi 877Si _o , i23) i3, L a F eii _i8 Sii _i2 , La (Fe _θi 8sSi _θi i2) i3H _θi 5, La (Fe _θi 8sSi _θi i2) i3Hi _iθ , LaFeH ₁₇ SiI ₁₃ Hi ₁ I, LaFeii _i57 Sii _i43 Hi _i3 , La (Fe _θi88 Si _θi i2) Hi _i5 , LaFeH ₁₂ Co ₀₁₇ SiI ₁ I, LaFeH ₁₅ AIi ₁₅ Co ₁ I, LaFeii _i5 Ali _i5 C _0i2 , LaFeii _i5 Ali _i5 C _0i4 , LaFen _i5 Ali _i5 Co _0i5 , La (Fe ₀₁₉₄ Co ₀₁₀₆ ) H _1S sAIi ₁ I ₇ , La (Fe ₀₁₉₂ Co _010S ) H _1S sAIi ₁ I ₇ .

Suitable manganese-containing compounds are MnFeGe, MnFe ₀₉ Co ₀ iGe,

MnFe _0i8 Co _0i2 Ge, MnFe _0i7 Co _0i3 Ge, MnFe _θi 6Co _θi4 Ge, MnFe _o , ₅ Co _0i5 Ge, MnFe _θi4 Co _θi6 Ge,

MnFe _0i3 Co _0i7 Ge, MnFe _0i2 Co _0i8 Ge, MnFe _0i i ₅ Co _0i85 Ge, MnFe _θi iCo _o , ₉ Ge, MnCoGe, Mn ₅ Ge _2i5 Si _o , ₅ , Mn ₅ Ge ₂ Si, Mn ₅ Gei, ₅ Sii, ₅ , Mn ₅ GeSi ₂ , Mn ₅ Ge ₃ , Mn ₅ Ge ₂ , ₉ Sb _o , i, Mn ₅ Ge ₂₁₈ SbO ₁₂ , Mn ₅ Ge ₂₁₇ Sb ₀₁₃ , LaMn _1i9 Fe _0i iGe, LaMn ₁₁₈₅ Fe ₀₁ I ₅ Ge, LaMn ₁₁₈ Fe ₀₁₂ Ge, (Fe _Oi 9Mn _Oi1 ) 3C, (Fe _o , ₈ Mn _{Oi 2} ) ₃ C, (Fe ₀₁₇ Mn ₀₁ S) ₃ C, Mn ₃ GaC, MnAs, (Mn, Fe) As, Mn _{1 + δ} As _0i8 Sb _0i 2, MnAs _0i75 Sb _0i25 , Mn ₁₁₁ As ₀₁₇₅ Sb ₀₁₂₅ , Mn _1i5 As _o , ₇₅ Sb _o , ₂₅ .

According to the invention suitable Heusler alloys are, for example, Fe ₂ MnSi ₀₅ Ge _05, Ni ₅₂₉ Mn ₂₂₄ Ga ₂₄₁₇ N i ₅₀₉ Mn _{24 7} Ga _24i4, Ni _55i2 Mn _{18 6} Ga ₂ 6 _i2, Ni _{51 6} Mn ₂₄₇ Ga ₂₃₁₈

Ni ₅₂ , ₇ Mn _23i9 Ga _23i4 , CoMnSb, CoNb _o , ₂ Mn _0i8 Sb, CoNb _0i4 Mn _0i6 SB, CoNb _0i6 Mn _0i4 Sb, Ni ₅₀ Mn ₃₅ Sn ₁₅ , Ni ₅₀ Mn ₃₇ Sn ₁₃ , MnFeP _o , ₄₅ As _o , ₅₅ , MnFeP _o , ₄₇ As _o , ₅₃ , Mn ₁₁₁ Fe ₀₁₉ P ₀₁₄₇ As ₀₁₅₃ , MnFeP _0i89-χ Si _χ Ge ₀ , π, χ = 0.22, χ = 0.26, χ = 0.30 , χ = 0.33.

The invention also relates to a metal-based magnetic cooling material obtainable by a method as described above.

In addition, the invention relates to a metal-based material for magnetic cooling, as defined above by means of the composition, excluding As containing materials, with an average crystallite size in the range of 10 to 400 nm, more preferably 20 to 200 nm, in particular 30 to 80 nm The average crystallite size can be determined by X-ray diffraction. If the crystallite size becomes too small, the maximum magnetocaloric effect is reduced. if the crystallite size is too large, however, the hysteresis of the system increases.

The metal-based materials according to the invention are preferably used in the magnetic cooling, as described above. A corresponding refrigerator has in addition to a magnet, preferably permanent magnets, metal-based materials, as described above. The cooling of computer chips and solar power generators is also considered. Further applications are heat pumps and air conditioning systems.

The metal-based materials produced by the process according to the invention may have any solid form. They may be present, for example, in the form of flakes, ribbons, wires, powders, as well as in the form of shaped bodies. Shaped bodies such as monoliths or honeycomb bodies can be produced, for example, by a hot extrusion process. For example, cell densities of 400 to 1600 CPI or more may be present. Also obtainable by rolling thin sheets are inventively preferred. Advantageous are non-porous molded body made of molded thin material, eg. As tubes, plates, nets, grids or rods. Shaping by metal injection molding (MIM) is possible according to the invention.

The invention is further illustrated by the following examples. Examples

example 1

Evacuated quartz ampoule, the pressed samples of MnFePGe were kept for 10 hours at 1100 ⁰ C to sinter the powder. This sintering was followed by annealing at 650 ^° C. for 60 hours to homogenize. However, instead of slowly cooling to room temperature in the oven, the samples were immediately quenched in water at room temperature. Quenching in water caused a degree of oxidation on the sample surfaces. The outer oxidized shell was removed by dilute acid etching. The XRD patterns show that all samples crystallize in a Fe ₂ P-type structure.

The following compositions were obtained:

Mn _{1: 1} Feo, 9Po, 8iGeo, i9; M and

Mn _{1 2} Feo, 8Po, 8iGeo, i9. The observed values for the thermal hysteresis are 7 K, 5 K, 2 K and 3 K for these samples in the order given. Compared to a slowly cooled sample which had a thermal hysteresis of more than 10 K, the thermal hysteresis could be greatly reduced become.

The thermal hysteresis was determined in a magnetic field of 0.5 Tesla.

Figure 1 shows the isothermal magnetization of Mn ₁ , iFe _o , 9B _o , 78Ge _o , 22 in the vicinity of the Curie temperature with increasing magnetic field. A field-induced transient behavior leading to a large MCE is observed for magnetic fields of up to 5 Tesla.

The Curie temperature can be adjusted by varying the Mn / Fe ratio and the Ge concentration, as well as the thermal hysteresis value.

The change in magnetic entropy calculated from the DC magnetization using the Maxwell relationship for a maximum field change of 0 to 2 Tesla for the first three samples is 14 J / kgK, 20 J / kgK and 12.7 J / kgK, respectively ,

The Curie temperature and the thermal hysteresis decrease with increasing Mn / Fe ratio. As a result, the MnFePGe compounds show relatively high MCE values in the low field. The thermal hysteresis of these materials is very small. Example 2

Melt spinning of MnFeP (GeSb)

The polycrystalline MnFeP (Ge, Sb) alloys were first prepared in a high energy ball mill and by solid phase reaction techniques as described in WO 2004/068512 and J. Appl. Phys. 99.08 Q107 (2006). The pieces of material were then placed in a quartz tube with a nozzle. The chamber was evacuated to a vacuum of 10 ^"2 mbar and then filled with argon gas of high purity. The samples were melted by high frequency and through the nozzle is sprayed by a pressure difference to a chamber with a rotating copper drum. The surface speed of the copper wheel was set and cooling rates of about 10 ⁵ K / s were achieved, and then the spun ribbons were annealed at 900 ^° C. for one hour.

X-ray diffractometry shows that all samples crystallize in the hexagonal Fe ₂ P pattern. Unlike samples prepared by the melt spinning method, no minor impurity phase of MnO was observed.

The values obtained for the Curie temperature, hysteresis and entropy were determined for different melt spinning peripheral speeds. The results are shown in Tables 1 and 2 below. In each case low hysteresis temperatures were determined.

Table 1 :

Table 2

Claims

claims

A process for producing metal-based materials for magnetic cooling or heat pumps, comprising the following steps

a) conversion of chemical elements and / or alloys in a stoichiometry, which corresponds to the metal-based material, in the solid and / or liquid phase,

b) optionally converting the reaction product from stage a) into a solid,

c) sintering and / or annealing the solid from step a) or b),

2. The method according to claim 1, characterized in that in step d) the quenching takes place at a cooling rate in the range of 200 to 1300 K / s.

3. The method according to claim 1 or 2, characterized in that the reaction in step a) takes place by heating the elements and / or alloys together in a closed container or in an extruder, or by solid phase reaction in a ball mill.

4. The method according to any one of claims 1 to 3, characterized in that the transfer takes place in a solid in step b) by melt spinning or spray cooling.

5. The method according to any one of claims 1 to 4, characterized in that in step c) is first sintered at a temperature in the range of 800 to 1400 ⁰ C and subsequently annealed at a temperature in the range of 500 to 750 ⁰ C.

6. The method according to any one of claims 1 to 5, characterized in that the metal-based material is selected from

(1) Compounds of the general formula (I) (AyBy-I) 2 _{+ δ} C _W D) c E _z (I) with the meaning

A Mn or Co,

B Fe, Cr or Ni,

C, D, E at least two of C, D, E are different from each other, have a non-vanishing concentration and are selected from P, B, Se, Ge, Ga, Si, Sn, N, As and Sb, where at least one of C, D and E is Ge or Si,

δ number in the range of -0.1 to 0.1

w, x, y, z are numbers in the range of 0 to 1, where w + x + z = 1;

Le (Fe _x Al _1-x ) ₁₃ H _y or La (Fe _x Si i _-x ) i ₃ H _y (II)

With

x number from 0.7 to 0.95

y number from 0 to 3;

La (Fe _x Al y CO _z ) ₁₃ or La (Fe _x Si _y Co _z ) ₁₃ (III)

With

x number from 0.7 to 0.95

y number from 0.05 to 1 - x

z number from 0.005 to 0.5;

LaMn _x Fe ₂ - _x Ge (IV) with x number from 1, 7 to 1, 95 and

(3) Heusler alloys of the type MnTP with T transition metal and P a p-doping metal with an electron count per atom e / a in the range of 7 to 8.5.

7. The method according to claim 6, characterized in that the metal-based material is selected from at least quaternary compounds of general formula (I), in addition to Mn, Fe, P and optionally Sb additionally Ge or Si or As or Ge and As or Si and As, or contain Ge, Si and As.

8. A metal-based material for magnetic cooling or heat pumps, obtainable by a process according to one of claims 1 to 7.

A metal-based material for magnetic cooling or heat pumping, obtainable by a process as defined in claim 6 or 7, excluding As-containing materials having an average crystallite size in the range of 10 to 400 nm.

10. Use of metal-based materials according to any one of claims 8 and 9 in the magnetic cooling, in heat pumps or in air conditioning systems.