DE69110644T2 - Process for modifying magnetic materials and magnetic materials made therefrom. - Google Patents

Abstract

A process is provided for modifying the magnetic properties of an intermetallic compound comprising at least iron, or a combination of iron with at least one transition metal, and at least one rare earth element. The process comprises heating the intermetallic compound in a reaction gas containing at least one element of groups IIIA, IVA or VIA of the Periodic Table in the gaseous phase to interstitially incorporate the element or elements of these groups into the crystal lattice of the intermetallic compound. Novel magnetic materials showing easy uniaxial anisotropy, increased spontaneous magnetization and Curie temperatures are produced by the process.

Description

The invention relates to a method for producing magnetic materials, to new and improved materials produced thereby and to the use of these materials to produce permanent magnets.

Magnets have many applications in engineering and science as components of devices such as electric motors, electric generators, focusing elements, lifting devices, locks, levitation devices, anti-friction fittings, and the like. For a magnetic material to be suitable for producing a permanent magnet, three intrinsic properties are of critical importance. These are the Curie temperature (Tc), i.e. the temperature at which a permanent magnet loses its magnetism, the spontaneous magnetic moment per unit volume (Ms), and the slight uniaxial anisotropy, which is conventionally represented by an anisotropy field Ba. The Curie temperature is of particular importance as it dictates the temperature below which a device containing the magnet must operate.

During this century, much research has been devoted to developing magnetic materials that combine high Curie temperatures and enhanced magnetic moments with severe uniaxial anisotropy. For many years, AlNiCo-type magnetic materials were used for practical applications in permanent magnets. In the late 1960s, it was discovered that alloys of the rare earth elements, particularly samarium, when alloyed with cobalt, can produce magnetic properties that made them superior to the AlNiCo type as permanent magnets. Samarium and cobalt compounds provided magnets that were particularly successful in many demanding practical applications requiring a magnet with a high energy product. However, the high cost of cobalt as a raw material led researchers in the early 1980s to consider the possibility of combining the cheaper and more abundant iron with the magnetically superior rare earth elements to produce permanent magnets with improved magnetic properties. A major breakthrough occurred in 1983 when Sumitomo Special Metals Company and General Motors of America independently developed a magnet material that combined a rare earth element and iron and incorporated a third element, boron, into the crystal lattice to obtain an intermetallic compound, Nd2Fe14B, which can be used to make magnets with an excellent energy product but a lower Curie temperature than the Sm-Co materials. These Nd-Fe-B magnet materials can have a Curie temperature of up to 320ºC and are particularly described in three European applications, EP-A-0101552, EP-A-0106948 and EP-A-0108474. Derivatives of these boride materials currently represent the state of the art in magnet technology. However, they are somewhat unstable in air and undergo chemical changes, gradually losing their magnetic properties, so that in practice they are not suitable for operation at temperatures above 150ºC, despite Curie temperatures of more than 300ºC.

The fact that the incorporation of boron into the crystal lattice of intermetallic materials containing a rare earth element and iron serves to improve magnetic properties has encouraged researchers to search for new compounds of other elements than boron in combination with rare earth elements and iron.

EP-A-344081 describes permanent magnet materials comprising a rare earth element and iron, wherein an additive of Si, Ti, Mo, B, W, V, Cr, Mn, Al, Nb, Ni, Sn, Ta, Zr and/or Hf is added as a replacement in a melting and casting process which produces materials with two finely divided phases. The materials allegedly exhibit improved magnetic properties.

EP-A-0320064 describes hard magnet materials containing neodymium and iron but having incorporated carbon, whereby compounds of the formula Nd₂Fe₁₄C are obtained with a similar crystal structure to the known boride materials. EP-A-0334445 describes modifications of the above type of material with incorporated carbon, in which neodymium is replaced with praseodymium, cerium or lanthanum and the iron is partially replaced by manganese. Finally, EP-A-0397264 describes compounds of the formula SE₂Fe₁₇C, in which SE is a combination of rare earth elements, at least 70% of which must be samarium. The preferred compound described in the last of the above three patent applications, in which carbon is interstitially incorporated into a Sm2Fe17 crystal lattice, exhibits improved Curie temperatures and uniaxial magnetic anisotropy. However, it is prepared by melting the individual components to obtain a cast which is then subjected to heat treatment at very high temperatures (900 to 1100°C) in an inert gas. The use of such a process limits the amount of additional elements that can be interstitially incorporated and the Curie temperatures that can be obtained.

A method for interstitial incorporation of an element of Group VA of the Periodic Table into intermetallic compounds containing one or more rare earth elements and iron has already been developed by the present inventors and is described in the applicants' co-pending European patent application No. 91303442.7, which process comprises heating the intermetallic starting material in a gas containing the element of Group VA in the substantial absence of oxygen.

Furthermore, heating compounds comprising a rare earth element and iron in a gas has previously been described by others, but there is no teaching that interstitial incorporation of another element has been achieved. For example, EP-A-0356279 describes improving magnetic properties of a thin strip of the above-described material suitable for magnetographic printing by heating the strip in a stream of oxygen at temperatures between 200 and 350°C. However, the effect of the oxygen is simply to form a rare earth oxide on the surface of the strip.

In 1987, Higano et al (IEEE Transactions on Magnetics, Vol. Mag 23 No. 5) reported an attempt to carry out a nitriding reaction by exposing Sm2Fe17 alloy powders to gaseous nitrogen at temperatures of 500 to 1100°C. However, it was found that the nitriding process simply decomposed the rare earth/iron alloy starting material, producing iron and nitrides of the rare earth elements. There was no visible evidence of the interstitially modified compound that had been intended.

A process has now been developed which allows interstitial incorporation of elements of groups IIIA, IVA and VIA of the periodic table into rare earth/iron type compounds to produce new materials with improved magnetic properties in terms of Curie temperatures (Tc), spontaneous magnetic moment per unit volume (Ms) and slight uniaxial anisotropy (Ba). Such materials are suitable for further processing to produce permanent magnets with a large energy product, which is more than 80 kJ/m³.

A method for interstitial modification of an intermetallic compound to improve the magnetic properties thereof comprises heating an intermetallic compound comprising at least iron or a combination of iron with at least one transition metal and at least one rare earth element in a reaction gas containing at least one element of Groups IIIA, IVA or VIA of the Periodic Table to a temperature of 400 to 650°C at a pressure of 0.01 to 1000 bar.

It is to be understood that the term rare earth element as used herein also includes the elements yttrium, thorium, hafnium and zirconium and that Groups IIIA, IVA and VIA of the Periodic Table are those defined by the CAS version of this System, i.e. Group IIIA B, Al, Ga, In, Tl; Group IVA C, Si, Ge, Sn, Pb; Group VIA O, S, Se, Te, Po.

The intermetallic compounds which can be modified by the process of the invention include those of the ThMn12 type having a tetragonal crystal structure and those of the Th2Ni17 or Th2Zn17 type having hexagonal and rhombohedral crystal structures, respectively. Those of the BaCd11 and CaCu5 crystal structure types can also be modified by the process.

In one embodiment of the invention, the intermetallic starting materials which are heated in a reaction gas according to the process of the invention can be tetragonal compounds of the general formula:

R(Tn-xMx)

where R is at least one rare earth element as defined herein, T is iron or a combination of iron with one or more transition metals, M is an element of Groups IVB, VB or VIB of the Periodic Table, n is approximately 12 and 0.5 < x < 3.0.

Preferred components for R are yttrium, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, erbium, thulium or lutetium or a mixture of two or more thereof. Particularly preferred compounds are those in which R is praseodymium or neodymium, such as, for example, PrFe₁₁Ti or NdFe₁₁Ti or compounds in which praseodymium or neodymium is combined with other rare earth elements. For example, in a compound such as NdFe₁₁Ti, some of the neodymium may be replaced by cerium to reduce cost or replaced by a heavy rare earth element such as terbium or dysprosium to improve uniaxial anisotropy.

In compounds of the formula R(Tn-xMx) described above, the iron can be present in combination with a transition metal such as cobalt, nickel or manganese. In particular, the iron can be replaced by up to 45% cobalt.

M is an early transition metal in groups IVB, VB and VIB of the periodic table and acts as a stabilizer element. Particularly preferred stabilizer elements are titanium, vanadium, molybdenum, tungsten or chromium.

In another embodiment of the invention, the intermetallic starting material which is heated in a reaction gas according to the process of the invention can be a hexagonal or rhombohedral compound of the general formula:

R'₂(T'n-x'M'x')

where R' is at least one rare earth element, T' is iron, M' is one or more transition metals, n is approximately 17 and 0 < x' ≤ 6.0.

Preferred components for R' for these hexagonal or rhombohedral starting materials are yttrium, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, erbium, thulium or lutetium or a mixture of two or more thereof and particularly preferred are those compounds wherein R is samarium such as, for example, Sm2Fe17 or wherein R is samarium partially replaced by neodymium, praseodymium or cerium.

Furthermore, a transition metal M', such as cobalt, nickel or manganese, can replace the iron.

In yet another embodiment of the invention, the intermetallic starting materials can be of the tetragonal crystal structure type BaCd₁₁, such as RFe₅Co₄M", where M" is a stabilizer element such as silicon, or of the crystal structure type CaCu₅, e.g. RCo₃FeM"', where M"' is a stabilizer element such as boron.

The preferred elements of Group IIIA, IVA or VIA, which are interstitially incorporated into the crystal lattice of the intermetallic compounds of the tetragonal, rhombohedral or hexagonal crystal structure described above can be are boron in group IIIA, one or more of carbon, silicon and germanium in group IVA and one or more of sulfur, selenium and tellurium in group VIA.

If necessary, the interstitially incorporated element can be combined with hydrogen.

The elements of groups IIIA, IVA or VIA which are incorporated interstitially, whether in combination with hydrogen or not, are designated Z below.

Thus, according to another aspect of the invention, there are provided novel magnetic materials of the general formula:

R(Tn-xMx)Zy

where R, T, x, M and z are as defined above and 0.1 < y < 1.0.

The invention also provides compounds of the general formula:

R'₂(T'n-x'M'x')Zy'

where R', T', M', Z and x' are as defined above and 0.5 < y' < 3.0, especially those where y' > 1.5. In the novel compounds of the invention, R' is samarium, Z is interstitially incorporated carbon and 2.0 < y < 3.0. Such compounds have Curie temperatures in the range of 668K.

The invention further provides compounds of the formula RTConx"M"x"Zy" wherein R, T, Z and M" are as defined above, n is 11, 1 <x"< 3 and 0 <y"< 1 and also compounds of the formula RCo₃FeM"'Z wherein R and Z as defined above and M"' is a stabilizer element such as boron.

The exact formula of the new materials will depend on the starting materials, which of course can exhibit all the variations already discussed above, and on the element or elements of Group IIIA, IVA or VIA of the Periodic Table that are present in the reaction gas.

For example, if the element Z is to be carbon, then the reaction gas may be a hydrocarbon such as methane, any C2 to C5 alkane, alkene or alkyne, or an aromatic hydrocarbon such as benzene. If the element Z is to be boron, then the reaction gas may be a boron-containing gas such as borane, diborane or decarborane vapor. If the element Z is silicon, then the reaction gas may be a silane and if the element Z is sulfur, then the reaction gas may be hydrogen sulfide. The reaction gas may be mixed with an inert carrier gas such as helium or argon.

Particularly preferred magnetic materials produced by the process of the invention are those in which the interstitially incorporated element is carbon, such as, for example, Sm2Fe17Cy', where y' > 2.0 and more preferably y = 2.5 or NdFe11TiCy and PrFe11TiCy, where 0.5 < y ≤ 1.0, preferably 0.6 < y < 0.9 and more preferably y = 0.8.

Other preferred magnet materials are those in which the interstitially incorporated element is boron, such as Sm2Fe17By', where y1 > 1.5.

To carry out the process according to the invention, a block of the intermetallic rare earth/iron starting material preferably comminuted to a fine powder having a particle size of less than 50 micrometers in diameter. Such a powder may optionally be prepared by mechanical alloying. The powder is then introduced into a suitable reaction vessel which is evacuated and filled with the reaction gas at a pressure of from 0.01 to 1000 bar. Typically the pressure is from 0.1 to 10 bar. The powder is then heated in the vessel in the presence of the gas to a temperature in the range from 400 to 650°C, and preferably about 500°C, for a period of time sufficient to permit diffusion of the element to be incorporated into the interstitial sites throughout each powder grain. The heating period may be any value up to 100 hours, but a suitable period can be readily determined from the diffusion constants of the interstitial atoms in the intermetallic compound. A typical heating period is from 2 to 10 hours.

Except in the case where the element to be interstitially incorporated is oxygen, it is preferred to heat the starting materials in the reaction gas in the substantial absence of oxygen.

After heating the reaction vessel is evacuated to remove excess reaction gas prior to cooling or alternatively it can be purged with an inert gas. The cooled product can then be processed to form permanent magnets. In the case of Sm₂Fe₁₇ ingots, for example, it has been found advantageous to include in the ingot up to 5 wt.% of an early transition metal additive. Suitable additives include niobium, zirconium or titanium. The additive suppresses the formation of alpha-Fe dendrites which occur because the phase does not melt congruently. Without the additive, the alpha-Fe phase, which tends to increase the coercivity in the interstitially modified material must be removed by a prolonged high temperature heat treatment at about 1000ºC.

It is an advantage of the new process according to the invention that interstitial incorporation of an element such as carbon, for example in a rare earth/iron intermetallic compound, can be achieved at a much lower temperature than in the arc melting process used in EP-A-0397264. Furthermore, the gas phase process of the invention allows a higher degree of interstitial incorporation to be achieved compared with the arc melting process. As a result, the uniaxial anisotropy is much larger and the Curie temperatures considerably higher than in materials produced by previously known processes.

Table I exemplifies the properties of compounds of the formula Sm₂Fe₁₇Cy prepared by the process described in EP-A-0397264 with compounds of this formula prepared by the process of the present invention. TABLE I Process of the present invention Compound produced Area Maximum Process Arc melting of elements Heating in hydrocarbon gas

From the above table the improvement of the magnetic properties of the compounds prepared by the process of the invention is evident.

The effect of interstitial incorporation of carbon in compounds of formula R₂Fe₁₇ on the crystal lattice parameters a(nm) c(nm), Curie temperature Tc(K), anisotropy and magnetic moment M(uβ/fu) is shown in Table II below. h represents compounds of hexagonal crystal structure and r compounds of rhombohedral crystal structure. The composition of the carbides is R₂Fe₁₇Cy', where y' is between 2.1 and 2.8. Table II Structure Anisotropy Level

The effect on magnetic properties and crystal lattice parameters of interstitial incorporation of carbon in compounds of the formula RFe₁₁Ti is shown in Table III below. In the table, the value of y is between 0.6 and 0.9. In preferred compounds, the value of y is 0.8. TABLE III Anisotropy at 300 K Axis Plane TABLE III (continued) Anisotropy Axis

The effects on magnetic properties of interstitial incorporation of boron into Sm2Fe17 and of carbon into Nd(Fe11Ti) are shown in Table IV below. TABLE IV light level

The interstitial incorporation of an element of Group IVA of the Periodic Table, for which the example is carbon, into selected intermetallic compounds of the formula R₂Fe₁₇₇ or RFe₁₇Ti and the altered properties thereby achieved are further shown in the figures in which:

Figure 1(a) shows the rhombohedral crystal structure of Sm₂Fe₁₇Cy', where site 9e is occupied by carbon and

Figure 1(b) shows the tetragonal crystal structure of Nd(Fe₁₁Ti)Cy, with site 2b shown as occupied by carbon;

Figure 2 shows the X-ray diffraction patterns of a Sm₂Fe₁₇ powder (a) before, (b) after treatment in methane for 2 hours at 550°C and (c) after treatment and orientation in a magnetic field of 0.3T. In Figure 2(b) a lattice expansion of about 6% is observed after an interstitial incorporation of carbon and in Figure 2(c) a slight anisotropy of the c-axis is shown after orientation;

Figure 3 shows the difference in cell unit volume between compounds with the formula R₂Fe₁₇Cy', where 1.5 < y' < 3.0 and those with the formula R₂Fe₁₇, where R is Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm or Lu. A significant increase in cell unit volume is observed for those compounds with the formula R₂Fe₁₇Cy';

Figure 4 shows the Curie temperature of compounds of the formula R₂Fe₁₇Cy', where 1.5 < y' < 3.0 and R₂Fe₁₇, where R is Ce, Pr, Nd, Sm, Cd, Tb, Dy, Ho, Er, Tm or Lu. A significant increase in the Curie temperature is observed for those compounds with the formula R₂Fe₁₇Cy';

Figure 5 shows room temperature magnetization curves of Sm₂Fe₁₇Cy' powder with 1.5 < y' < 3.0, which is magnetically aligned in an applied field of 1T and fixed in epoxy resin. The anisotropy field derived from the data shown in Figure 5 is 16T;

Figure 6 shows X-ray diffraction patterns of Sm₂Fe₁₇ before treatment (solid line) and after treatment (broken line) at 475ºC for 2 hours in benzene vapor, showing a lattice expansion of 5.5%,

Figure 7 shows the difference in unit cell volume between compounds with the formula R(Fe₁₁Ti) and compounds with the formula R(Fe₁₁Ti)Cy, where y is 0.6 < y < 0.9 and where R is Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm or Lu. A significant increase in unit cell volume is observed when carbon was interstitially incorporated by heating in butane;

Figure 8 shows the Curie temperatures of compounds of the formula R(Fe₁₁Ti) and R(Fe₁₁Ti)Cy, where 0.6 < y < 0.9, prepared by the process of the invention and where R is Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm or Lu. Again, a significant increase in the Curie temperature is observed when carbon is incorporated interstitially;

Figure 9 shows the X-ray diffraction pattern of an arc melted and non-heat treated Sm₂Fe₁₇ ingot containing 5 wt% Nb, which has a substantial absence of free iron. The solid line is the trace of the Sm₂Fe₁₇ ingot with additive and the dashed lines indicate where the α-Fe peaks would appear in an ingot without additive;

Figure 10 shows the variation of the anisotropy field as a function of the neodymium content for the series of compounds (Y1- Nd)(Fe₁₁Ti)C�0,₈.

From the data presented herein it is apparent that the process of the invention has considerable advantages over previously known processes for effecting interstitial incorporation of another element into rare earth/iron type intermetallic magnetic compounds and that the materials produced thereby have improved magnetic properties. In particular, the increase in Curie temperature, the uniaxial anisotropy and the increase in spontaneous magnetization make the compounds of the invention very suitable for the production of permanent magnets. The high Curie temperatures of these materials mean that magnets made from them can be used in devices or processes requiring high temperature conditions and that the magnetization of the Magnets are not lost.

Magnets can be formed from the materials of the invention by aligning the interstitially modified intermetallic compound in powder form in a magnetic field with a polymer resin to produce a polymer-bonded magnet. More specifically, the interstitially modified intermetallic compound powder can optionally be ground to a finer powder having a particle size of 10 µm or less and then mixed with a polymer material (e.g., a thermosetting resin or an epoxy resin) and optionally oriented in a magnetic field sufficient to align the easy axes of the powder granules. The resin is then cured and the composite is exposed to a high magnetizing field sufficient to saturate the remanent magnetization.

In a modification of this process, the composite can be formed into a desired shape by compression or injection molding before the magnetizing field is applied.

An alternative is to make the composite with a metal matrix instead of a polymer matrix. In this case, a low melting point metal such as Zn, Sn or Al or a low melting point alloy such as solder can be used. The metal is mixed with the ground intermetallic powder, which can be oriented in a magnetic field before heat treatment at a temperature sufficient to melt the metal and form a metal-metal composite. The preferred metal is zinc, which reacts with any free αFe to form a non-magnetic Fe-Zn alloy, thereby improving the coercivity of the magnet.

Another way in which magnets can be formed from the materials is by forging with a soft metal under stress that tends to mechanically orient the crystallites of the material. In particular, a shear stress can be applied to the intermetallic powder, which is optionally mixed with a soft metal such as Al. The shear stress aligns the c-axes of the intermetallic crystallites and thereby increases the remanent magnetization of the magnet.

Claims (29)

1. A process for interstitial modification of an intermetallic compound to improve the magnetic properties thereof, comprising heating an intermetallic compound comprising at least iron or a combination of iron with at least one transition metal, and at least one rare earth element in a reaction gas containing at least one element of groups IIIA, IVA or VIA of the Periodic Table to a temperature of 400 to 650°C at a pressure of 0.01 to 1000 bar. 2. The method according to claim 1, wherein the intermetallic compound has the general formula: R(Tn-xMx) wherein R is at least one rare earth element, T is iron or a combination of iron with at least one or more transition metals, M is an element of groups IVB, VB or VIB of the Periodic Table, n is approximately 12 and 0.5<x<3.0. 3. The method according to claim 1, wherein the intermetallic compound has the general formula: R'₂(T'n-x'M'x') wherein R' is at least one rare earth element, T' is iron, M' is one or more transition metals, n' is approximately 17 and 0< x'< 6.0. 4. The method of claim 2 or 3, wherein R is yttrium, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, erbium, thulium or lutetium or a mixture of two or more thereof. 5. A method according to claim 2 or 4, wherein R is neodymium or praseodymium or a combination of neodymium or praseodymium with one or more rare earth elements. 6. A process according to claim 3 or 4, wherein R' is samarium or samarium in combination with one or more rare earth elements. 7. A method according to claim 2, 4 or 5, wherein the iron is in combination with one or more of cobalt, nickel and manganese. 8. A method according to any one of claims 2, 4, 5 or 7, wherein M is titanium, vanadium, molybdenum, tungsten or chromium. 9. A process according to any one of claims 3, 4 or 6, wherein M' is cobalt, nickel or manganese or a combination of two or more thereof. 10. A method according to any one of the preceding claims, wherein the element of Group IIIA, IVA or VIA which is interstitially incorporated into the intermetallic compound is boron, carbon, silicon, germanium, sulfur, selenium or tellurium or a combination of two or more thereof. 11. A process according to any one of claims 1 to 9, wherein, unless the element to be interstitially incorporated is oxygen, the intermetallic starting material in the reaction gas is heated in the substantial absence of oxygen. 12. The process according to claim 10 or 11, wherein the element of Group IVA which is interstitially incorporated is carbon and the reaction gas is a hydrocarbon. 13. The process of claim 12, wherein the reaction gas is methane, a C2 to C5 alkane, alkene or alkyne or an aromatic hydrocarbon. 14. The method according to claim 12 or 13, wherein the prepared interstitially modified compound has the formula: Sm₂Fe₁₇Cy' where 0.5< y< 3.0. 15. The method according to claim 12 or 13, wherein the prepared interstitially modified compound has the formula: PrFe₁₁TiCy or NdFe₁₁TiCy where 0.5< y< 1.0. 16. The process according to claim 10 or 11, wherein the Group IIIA element that is interstitially incorporated is boron and the reaction gas is borane or decaborane. 17. The method of claim 16, wherein a prepared interstitially modified compound has the formula: Sm₂Fe₁₇By' where 0.5< y'< 3.0. 18. The method according to claim 10 or 11, wherein the element of Group IVA that is interstitially incorporated is silicon and the reaction gas is a silane. 19. The process according to claim 10 or 11, wherein the element of Group VIA which is interstitially incorporated is sulfur and the reaction gas is hydrogen sulfide. 20. A process according to any one of the preceding claims, wherein the intermetallic compound is ground to a powder having a particle size of less than 50 micrometers in diameter prior to heating in the reaction gas. 21. A process according to any one of the preceding claims, wherein the intermetallic compound comprises as additive up to 5% by weight of an element of groups IVB, VB and VIB of the Periodic Table. 22. The method of claim 21, wherein the additive is niobium, zirconium or tantalum. 23. A process for producing a permanent magnet, wherein a powder of the interstitially modified material produced by the process according to any one of claims 1 to 22 is magnetically or mechanically aligned and formed into a magnet. 24. The method of claim 23, wherein a permanent magnet is formed by (a) orienting the interstitially modified intermetallic compound in powder form in a magnetic field with a polymer resin to form a polymer-bonded magnet or (b) orienting the interstitially modified intermetallic compound in powder form in a magnetic field, mixing with a low-melting metal or alloy and heating to form a metal-bonded magnet or (c) Forging the interstitially modified intermetallic compound in powder form with a soft metal under stress that magnetically orients the material to form a metal-bonded magnet. 25. Magnetic material of general formula: R(Tn-xMx)Zy, where R is at least one rare earth element, T is iron or a combination of iron with one or more transition metals, M is an element of groups IVB, VB or VIB of the Periodic Table, Z is one or more elements of groups IIIA, IVA or VIA of the Periodic Table, n is approximately 12 and 0.5< x< 3.0 and 0.1< y&le;1.0, characterized in that Z is interstitially incorporated into the crystal lattice of the material. 26. Magnetic material of general formula: R'₂(T'n-x'M'x')Z'y', where R' is samarium, T' is iron, M' is one or more transition metals, Z is carbon which is interstitially incorporated into the crystal lattice of the material, n is approximately 17 and 0&le;x'< 6.0, characterized in that 2.0<y< 3.0 and that the magnet material has a Curie temperature in the range of 668 K. 27. Use of a magnetic material according to claim 25 or claim 26 for producing permanent magnets. 28. Use of the product of the process according to one of claims 1 to 22 for producing permanent magnets. 29. Permanent magnet made from the product of the process according to any one of claims 1 to 22.