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The congregation of Nd-rich phases on the surfaces of sintered Nd–Fe–B magnets is observed in this work. The thickness of the Nd-rich congregated layers is about 20–60 μm. The congregated phases in the base plane and hard plane are quite different. On the base plane, the gain boundary in the surface layer is obscure. On the hard plane, a strange structure like eutectic phase can be found between the matrix and the surface. This behavior of Nd-rich phases can be comprehended by referring to thermodynamics.

Nanocrystalline two-phase Nd9Fe85.5Nb1.0B4.5-yCy magnets (y=0.5-4.5) have been prepared by melt spinning and subsequent heal treatment. The effect of remanence enhancement has been observed in the melt-spun ribbons after a proper annealing procedure. A two-phase nanocomposite Nd9Fe85.5Nb1.0B4.0C0.5 magnet with optimum magnetic properties of H-cj.=6.6 kOe, J(r)=10.22 kGs and (BH)(max)=13.32 MGOe has been obtained. (C) 2001 Elsevier Science B.V. All rights reserved.

A novel Tb3(Fe,Cr)29 single crystal, which has a monoclinic Nd3(Fe,Ti)29-type structure, is obtained using the Czochralski method by performing a proper heat treatment on the Tb2Fe16.46Cr1.23 crystal with a Th2Ni17-type structure. Thermomagnetic curves along the easy axis and magnetization curves along the easy and hard axes are presented for both crystals. The lattice parameters are a = 1.058 nm, b = 0.848 nm, c = 0.968 nm, α = γ = 90°, and β = 96.93° for the Tb3(Fe,Cr)29 single crystal. The Curie temperatures, saturation magnetizations, and magnetocrystalline anisotropy constants are compared between the Tb-2:17 and Tb-3:29 crystals. The magnetization behavior along the hard axis is quite different as a first-order magnetization process (FOMP) of type I for the Tb-2:17, but a FOMP of type II for the Tb-3:29 crystal is observed below room temperature. At low temperatures, magnetohistory effects are detected for both crystals.

A novel Y3(Fe,Cr)29 single crystal with the Nd3(Fe,Ti)29-type structure has been successfully prepared using the Czochralski method followed by a heat treatment on a Y2Fe15Cr2 single crystal with a Th2Ni17-type structure. The magnetization curves measured along the easy and hard direction in the temperature range from 1.5 to 293 K are presented. The lattice parameters of the crystal are a = 10.645 A, b = 8.455 A, c = 9.678 A and = 97.462°, respectively. The Curie temperature is 410 K. The saturation magnetizations decrease with increasing temperatures and are in good agreement with the spin-wave relation. The average magnetic moment is 1.54 µB per Fe atom at 1.5 K. The crystal keeps a planar anisotropy from 1.5 to 293 K. The magnetocrystalline anisotropy constants at 1.5 K are K1 = -0.87 × 106 J m-3 and K2 = 0.19 × 106 J m-3.

A Tb-3(Fe,Cr)(29) single crystal with the monoclinic Nd-3(Fe,Ti)(29)-type structure was obtained after proper heat treatment on the original single crystal with a hexagonal structure grown by the Czochralski method. The magnetization curves along the hard and easy directions are presented. The lattice parameters are a = 1.058 nm, b = 0.848 nm, c = 0.968 nm, alpha = gamma = 90 degrees, and beta = 96.93 degrees, respectively. The Curie temperature is 477 K and the saturation magnetizations are 51.74 A m(2)/kg (18.07 mu(B)/f.u.) at 1.5 K and 58.34 A m(2)/kg (20.38 mu(B)/f.u.) at 293 K, respectively. Below room temperature, a first-order magnetization process of type II occurring at the critical field of 6.0 T at 100 K and 5.5 T at 200 K was observed. A magnetohistory effect taking place at about 175 K was also detected on the Tb-3(Fe,Cr)(29) single crystal. (C) 1999 Elsevier Science Ltd. All rights reserved.

In the present paper, based on the investigation of the structure and magnetic properties of the compounds RFe11.35Nb0.65Cy (R=Y, Tb, Dy, Ho, Er) and YxDy1−xFe11.35Nb0.65Cy (x=0,0.4,0.6,0.8,1.0) and their parent compounds, a study of the effect of the volume change due to carbonation on the Curie temperature of these compounds has been performed. The d ln TC/d ln V values were derived by comparing the Curie temperature and volume before and after carbonation. Our results indicate that the relationship between d ln TC/d ln V and the Curie temperature TC can be well described in terms of the itinerant-model formalism.

A Y2Fe15Cr2 Single crystal with the Th2Ni17-type structure has been prepared by the Czochralski method and investigated by means of Laue back-reflection, metallographic observation, X-ray diffraction, the singular point detection technique and magnetic measurements. A magnetohistory effect has been observed at a low temperature. Magnetization curves have been measured along the easy and hard directions in fields up to 6.5 T, The saturation magnetization and magnetocrystalline anisotropy field decrease with increasing temperature. The experimental magnetocrystalline anisotropy constant is in good a,areement with the calculation results on first approximation. (C) 1999 Elsevier Science Ltd. All rights reserved.

The variation in crystallographic and magnetic properties with Dy concentration has been investigated on Y 1−x Dy x Fe 11 Mo and Y 1−x Dy x Fe 11 MoN y compounds in detail. Lattice parameters a, c and saturation magnetization M s at 1.5 K decrease while the Curie temperature T c slightly increases with increasing Dy concentration in Y 1−x Dy x Fe 11 Mo system. At room temperature, all Y 1−x Dy x Fe 11 Mo samples exhibit a uniaxial anisotropy, and the anisotropy field decreases with increasing Dy concentration. Upon nitrogenation, the nitrides Y 1−x Dy x Fe 11 MoN y retain the tetragonal structure symmetry of ThMn12 type with the addition of an expansion of about 4% on the unit cell volume. The Curie temperature and saturation magnetization at 1.5 K are drastically enhanced by nitrogenation. Unlike the parent alloy, YFe 11 MoN y shows a canted anisotropy at room temperature. But the other Y 1−x Dy x Fe 11 MoN y compounds with x⩾0.2 have a uniaxial anisotropy which becomes stronger with increasing Dy concentration.

Sm3Fe26.7V2.3N4 nitrides and Sm3Fe26.7V2.3Cy carbides have been synthesized by gas-solid phase reaction. Their hard magnetic properties have been investigated by means of additional ball-milling at room temperature. The saturation magnetization of Sm3Fe26.7V2.3N4 almost decreases linearly with increasing ball-milling time t, but that of Sm3Fe26.7V2.3Cy has no obvious change when the ball-milling time increases from t = 1 to 28 h. As a preliminary result, the maximum remanence B-r of 0.94 and 0.88 T, the coercivity mu(0i)H(C) of 0.75 and 0.25 T, and the maximum energy product (BH) of 108.5 and 39.1 kJ/m(3) for their resin-bonded permanent magnets are achieved, respectively, by ball-milling at 293 K. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

A Tb2(Fe,Cr)17 single crystal with the Th2Ni17-type structure has been prepared by the Czochralski method and investigated by means of Laue back-reflection, metallographic observation, x-ray diffraction and magnetic measurements. The magnetization curves along the easy and hard directions in the temperature range from 5 K to 293 K are presented. The spontaneous magnetization increases with increasing temperature below 300 K. A magnetohistory effect was observed below 167 K. A first-order magnetization process (FOMP) of type I was also observed below 250 K. The FOMP critical fields occur at about 5.5 T at low temperature.

The variation of the crystallographic and magnetic properties with Dy concentration has been investigated for Nd 1− x Dy x Fe 10.5 Mo 1.5 and Nd 1− x Dy x Fe 10.5 Mo 1.5 N y compounds. In the Nd 1− x Dy x Fe 10.5 Mo 1.5 system, the lattice parameters a , c and the saturation magnetization at 1.5 K decrease with increasing Dy concentration, while the Curie temperature changes only little. At room temperature, all Nd 1− x Dy x Fe 10.5 Mo 1.5 samples exhibit weak easy-axis anisotropy with anisotropy fields up to about 1 T with a clear increase with increasing Dy concentration. Upon nitrogenation, the Nd 1− x Dy x Fe 10.5 Mo 1.5 N y compounds retain the original tetragonal ThMn 12 -type of structure but the unit-cell volume increases about 3.1%. At room temperature, the Nd 1− x Dy x Fe 10.5 Mo 1.5 N y compounds show easy-axis anisotropy with anisotropy fields above 7.2 T. At room temperature, in the Nd 1− x Dy x Fe 10.5 Mo 1.5 N y system the anisotropy field slightly increases with increasing Dy concentration.

The magnetocrystalline anisotropy and the spin reorientation of Sm1−xDyxFe10.5Mo1.5 were investigated in detail. At room temperature, all Sm1−xDyxFe10.5Mo1.5 alloys possess easy c-axis anisotropy and the magnetocrystalline anisotropy field decreases with increasing Dy concentration. However, at low temperature, a spin reorientation transition of axis-to-cone type was observed in the Sm1−xDyxFe10.5Mo1.5 alloys with x ≥ 0.8. The spin reorientation temperatures increase with increasing Dy concentration in the Sm1−xDyxFe10.5Mo1.5 alloys.

Interstitial rare-earth iron-rich Sm 3 (Fe,Cr) 29 X y (X=N, C) compounds with the monoclinic Nd 3 (Fe,Ti) 29 structure have been successfully synthesized by gas–solid reaction. An intrinsic coercivity μ 0i H c of ∼0.80 T at 293 K has been attained for both the nitride and carbide prepared by ball-milling. The intrinsic coercivity μ 0i H c of the nitride powder increases with decreasing average particle size d and exhibits a maximum at d =0.4 μm, then decreases slowly for smaller d values. Our results suggest that the coercivity of the Sm 3 Fe 24 Cr 5 N y powder is mainly controlled by a nucleation mechanism as observed in the Sm 3 (Fe,Ti) 29 N y and 2:17:N nitrides. A remanence of B r =O.87 T has been achieved at 293 K for Sm 3 Fe 24 Cr 5 N y which gives an energy product of (BH) max =l04.8 kJ/m 3 . Similar hard magnetic properties were observed for the carbide powder. The temperature coefficient of the remanence of the carbide is worse than that of Nd–Fe–B, although it has a better temperature coefficient of coercivity. Both the nitride and carbide powders have better corrosion resistance than commercial Nd–Fe–B powder.

The variation in crystal structure and intrinsic magnetic properties with Y concentration has been investigated for the Dy 1− x Y x Fe 11 Mo system in detail. The lattice parameters a , c of Dy 1− x Y x Fe 11 Mo slightly increase while the Curie temperatures decrease with increasing Y concentration. At room temperature, all Dy 1− x Y x Fe 11 Mo samples exhibit a uniaxial magnetocrystalline anisotropy. The anisotropy field is enhanced slightly by increasing the Y concentration at room temperature. A spin reorientation transition was observed at low temperature for the Dy 1− x Y x Fe 11 Mo samples with x =0–0.8, and the spin reorientation temperature decreases with increasing of Y concentration.

The series has been investigated by means of x-ray diffraction, thermomagnetic analysis, vibrating sample magnetometer, SQUID magnetometer and the singular-point detection technique. With increasing Mo concentration, lattice parameters a, c and V increase linearly, while Curie temperature and saturation magnetization decreases markedly. A value of of has been obtained for the hypothetical compound. All the samples show uniaxial anisotropy at room temperature. A maximum appears at x = 1.5 on the curve of magnetocrystalline anisotropy field versus Mo concentration at room temperature. At low temperature, compounds have a complex magnetic behaviour. A transition from uniaxial anisotropy to canted structure at low temperatures in samples with low Mo concentration (x < 2) and magnetohistory effects in samples with high Mo concentration were observed.

In the present paper, a study of the effect of the volume change on the Curie temperature ( T C ) of R(Fe,M) 12 (M=Nb, Ti and V) due to nitrogenation has been performed. The dln T C /dln V values were derived by comparing the Curie temperatures and volumes before and after nitrogen. Our results indicate that the relationship between dln T C /dln V and the Curie temperature T C agrees with an itinerant-model formalism. The effects of volume expansion and the increasing electron correlation play important roles in the enhancement of the Curie temperature upon nitrogenation of intermetallic compounds.

The novel ternary rare-earth iron-rich interstitial compounds R 3 (Fe,Cr) 29 X y (R=Nd, Sm and X=N, C) with the monoclinic Nd 3 (Fe,Ti) 29 structure have been successfully synthesized. Introduction of the interstitial nitrogen and carbon atoms led to a relative volume expansion ΔV / V of about 6% and an enhancement of Curie temperatures T c about 268 K for the nitride and about 139 K for the carbide, respectively. The Nd 3 Fe 24.5 Cr 4.5 X y compounds have a planar anisotropy at room temperature. A first-order magnetization process (FOMP) with critical field B cr =4.4 T and 3.1 T at room temperature were observed for the Nd-nitride and carbide compounds, respectively. The Sm 3 Fe 24 Cr 5 X y compounds were found to have a large uniaxial anisotropy of about 18 T at 4.2 K and about 11 T at 293 K. A FOMP with B cr =2.3 T was also observed in the Sm-nitride compounds at 4.2 K. Magnets with coercivity of μ Oj H c ∼0.8 T at 293 K has been successfully developed from the Sm 3 Fe 24 Cr 5 X y (XN and C) phases.

The dependence of remanence and coercivity on the magnetizing field is studied for isotropic and anisotropic epoxy resin bonded magnets. It was found that the coercivity of the NdFe 10 Mo 2 -N bonded magnet is mainly controlled by nucleation of reversed magnetic domains. Variation of iH c with Zn content and heat treatment conditions is studied. The value of μ0i H c obtained in the best Zn-bonded condition is about 0.15 T higher than before bonding. The variation of the amount of α-Fe with processing conditions is demonstrated for anisotropic Zn-bonded magnets.

In the present paper, based on the investigation of the structure and magnetic properties of PrFe 12-x Mo x N y and their parent compounds, the effect of the volume change due to nitrogenation on the Curie temperature of these compounds has been studied. The d ln T C /d ln V values were derived by comparing the change of Curie temperature and volume before and after nitrogenation. Our results indicate that the relationship between d ln T C /d ln V and the Curie temperature Tc agrees with the Brouha-Buschow equation very well. The decrease of Curie temperature with increasing Mo concentration in the systems of PrFe 12-x Mo x and their nitrides may be explained by the Mohn-Wohlfarth model considering the spin fluctuation effect.

The novel nitride with monoclinic structure is synthesized by gas - solid reaction. Its hard magnetic properties have been investigated by ball milling and magnetic measurements. The intrinsic coercivity increases with decreasing average particle size d and, after reaching a maximum at , then decreases slowly. increases also with increasing magnetizing field. A value of has been attained. The magnetizing field for obtaining coercivity saturation is about 1.5 T. The hard magnetic properties of remanence and energy product for are achieved at 293 K.

Room-temperature 57Fe Mossbauer spectra have been measured in Sm2Fe17 under different heat treatment conditions. The details of fitting these spectra is exhaustively discussed. The spectra of Sm2Fe17 are split into seven inequivalent magnetic sites. An identical result was obtained by using two fitting modes. The following has been indicated from the results for all samples. Firstly for these samples containing α-Fe sextets and paramagnetic doublets, by choosing an appropriate annealing system, the smallest amount of impurities might be obtained, i.e. an approximately single-phase Sm2Fe17 compound was obtained. Secondly the overall weighted average fields were all approximately equal. This was thought to arise because the different heat treatment conditions caused no change in the near-neighbour coordination of iron atoms. Thirdly the 6c site and 18 h site had the largest and the smallest hyperfine fields, respectively.

The coercivity behaviour of bonded magnets made from sieved inert-gas-atomized Nd(Dy) - Fe - B powders has been investigated. For magnets with particle sizes , the coercivity is controlled by a nucleation mechanism as in the sintered magnet. For the magnet with particle sizes of , the hardening mechanism is mainly controlled by nucleation as in the sintered magnet but the hardening mechanism of domain wall pinning or the nucleation of a single domain, which usually appears in melt-spun materials, may also be involved. The coercivity behaviour of bonded magnets made from gas-atomized powders seems to be between those of the sintered and melt-spun magnets depending on the particle size. Meanwhile it has been found that the demagnetizing field of bonded magnets made from the inert-gas-atomized powders is very small.

A new series of compounds, Gd x Dy 1− x Fe 11.35 Nb 0.65 , with a ThMn 12 structure was synthesized. The corresponding nitrides prepared by gas solid reaction retain the structure of their parent alloys, but with an expansion of 3% of the unit cell volume. Their Curie temperature increases by about 200 K. For the alloys, the spin-reorientation transition temperature T sr1 decrease, while the Curie temperature and the magnetocrystalline anisotropy field increase with the substitution of Gd for Dy. Upon nitrogenation, the spin reorientation of the nitrides disappear, and the magnetocrystalline anisotropy field of the nitrides decrease with increasing Gd content.

A new series of the carbides RFe11.35Nb0.65Cy (R identical to Y, Gd, Tb, Dy, Ho or Er) (y approximately=1.0) with the ThMn12 structure was synthesized by gas-solid-phase reaction at 773 K. The unit-cell volumes of the carbides increase upon carbonation by nearly 4.0% across the series. The average enhancement of the Curie temperature is about 160 K. The highest Curie temperature is 733 K for the carbide GDFe11.35Nb0.65Cy. The saturation magnetization of the Fe sublattice is 22.5 mu B FU-1 at 4.2 k and 20.7 mu B FU-1 at room temperature. The maximum value of the anisotropy field found at room temperature for DyFe11.35Nb0.65Cy is about 8 T.

The X-ray diffraction pattern of the novel Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound was indexed on the basis of monoclinic symmetry with the lattice parameters a = 1.065 nm, b = 0.858 nm, c = 0.972 nm and β = 96.98°. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound exhibits ferromagnetic ordering with T C = 486 K and a planar anisotropy. The new interstitial nitride of the Sm 3 (Fe 0.933 Ti 0.067 ) 29 N 5 compound was obtained by gas-solid phase reaction. The nitride has the same structure as the parent compound. The introduction of nitrogen leads to an increase in the Curie temperature to 750 K. The saturation magnetization values σ s = 160 A m 2 kg −1 at 4.2 K and 140 A m 2 kg −1 at 293 K. The anisotropy was changed from planar to uniaxial upon nitrogenation. The anisotropy field B a values were 18.1 T at 4.2 K and 12.8 T at 293 K. The hard magnetic properties of the Sm 3 (Fe 0.933 Ti 0.066 ) 29 N 5 compound have been studied. A coercivity μ 0i H c value of 0.83 T and a maximum energy product ( BH ) max of 105 kJ m −3 at 293 K have been achieved. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 Ny compound is a promising material for permanent magnetic applications.

In the present paper the diffusion behavior of nitrogen in Sm 2 Fe 17 has been investigated. The Curie temperatures of nitrides are experimentally found to vary in a very narrow temperature range. No other intermediate nitride with a small Curie temperature has been found. After the further annealing of non-fully nitrided powder in an Ar atmosphere, some of the nitrogen atoms, which have weak interactions with the interstitial site, can be excited from interstitial sites of Sm 2 Fe 17 molecule by thermal energy and migrate again. However, some of nitrogen atoms are still located at interstitial sites of Sm 2 Fe 17 molecule owing to the strong interaction between gas atoms and the interstitial site. In the nitrogen diffusion process, with increasing occupation of the interstitial site in Sm 2 Fe 17 by nitrogen atoms, the diffuse force for nitrogen atom decreases owing to the change in the chemical potential of system, which results in different diffusive activities of nitrogen atoms under different nitrogen absorption contents x in Sm 2 Fe 17 N x . Meanwhile the particle size dependence of the diffusion behavior has also been discussed. The surface and the grain boundary diffusion modes play important roles in the diffusion process of nitrogen atoms into Sm 2 Fe 17 particles especially for small particles.

Two new compounds of the type RFe 11.4 Nb 0.6 (R = Y, Gd) with ThMn 12 structure were synthesized. The corresponding nitrides retain the same structure as their parent alloys, but with an expansion in the unit cell volume of about 3%. The temperature dependences of saturation magnetization and anisotropy field were determined from 4.2 K to room temperature for the Y compound and its nitride. The Curie temperature is 597 K for GdFe 11.4 Nb 0.6 and 773 K for its nitride. The effect of the third stabilizing element on the Curie temperature of ThMn 12 -type ternary rare-earth iron-rich compounds was investigated and discussed in terms of a diagonal positional relationship in the periodic table of the elements.

The formation and magnetic properties of a novel intermetallic Sm3(Fe0.933Ti0.067)29 compound and the Sm3(Fe0.933Ti0.067)29Ny (y=5) nitride have been investigated. The x-ray diffraction patterns of the nitride and the parent compound were indexed on the basis of the Nd3(Fe,Ti)29-type structure with monoclinic symmetry. The parent and the nitride exhibit ferromagnetic ordering with a Curie temperature TC of 486 K for the parent and 750 K for the nitride. Introduction of nitrogen led to an increase in saturation magnetization; Ms for the nitride is 160 A m2 kg-1 at 4.2 K and 140 A m2 kg-1 at 293 K. The nitride has a uniaxial anisotropy with an anisotropy field strength Ba for 25 T at 4.2 K and 12.8 T at 293 K. The coercivity mu 0iHc=0.83 T at 293 K for this new nitride has been determined.

A series of compounds with the ${\mathrm{ThMn}}_{12}$-type structure, R${\mathrm{Fe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ (R=Y, Sm, Gd, Tb, Dy, Ho, Er, and Lu), were synthesized. The corresponding nitrides, obtained by gas-solid reactions, retained the same structure as their parent compounds, but with a relative volume expansion of 3%. The Nb atoms occupy the 8i sites in the ${\mathrm{ThMn}}_{12}$ structure. The highest Curie temperatures are 597 K and 773 K for ${\mathrm{GdFe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ and its nitride, respectively. The average iron magnetic moment ${\mathrm{\ensuremath{\mu}}}_{\mathrm{Fe}}$ at T=1.5 K is 1.9${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ for parent compounds and 2.1${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ for the nitrides. By the introduction of nitrogen, the Fe-Fe exchange interaction is much strengthened while the R-Fe exchange interaction is slightly weakened. The enhancement of ${\mathrm{\ensuremath{\mu}}}_{\mathrm{Fe}}$ by the influence of interstitial nitrogen is about 11%. The Fe sublattices of R${\mathrm{Fe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ compounds and their nitrides have an easy c-axis anisotropy. At T=1.5 K, the anisotropy constant ${\mathit{K}}_{1}$(Fe) is 25.7 K/f.u. for the parent compounds and 21.9 K/f.u. for the nitrides. The reduction of ${\mathit{K}}_{1}$(Fe) by the influence of interstitial nitrogen is about 17%. Spin-reorientation transitions were observed in ${\mathrm{DyFe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ and ${\mathrm{ErFe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ compounds. The complex magnetic behavior of R${\mathrm{Fe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ at low temperatures can be explained by exchange and crystal-field-interaction models. The ${\mathrm{SmFe}}_{11.35}$${\mathrm{Nb}}_{0.65}$ compound has an anisotropy field of 10.0 T at room temperature. Its high Curie temperature and magnetization make it a potential candidate for applications as a permanent magnet.

Nd 1+ x Fe 10 Mo 2 N y nitrides with permanent magnetic properties were prepared by heating fine Nd Fe Mo particles in an N 2 atmosphere followed by milling. The best composition and nitriding and milling conditions to obtain a high coercivity and energy product for the nitrides were investigated. H c and B r of magnetically aligned samples increased and decreased monotonically respectively with increasing milling time after nitriding irrespective of composition and nitriding conditions. The room temperature properties μ o H c = 0.7 T, B r = 0.4 T and ( BH ) max = 42 kJ m −3 were obtained.

In the present paper, the structure and magnetic properties of TbMn6Sn6 have been investigated. TbMn6Sn6 is found to be of HfFe6Ge6-type structure (space group P6/mmm) with a = 5.5461 Angstrom, c = 9.0477 A and V = 241 Angstrom(3). This compound shows ferrimagnetic behaviour with the ordering temperature T-c = 421 K. A peak is also observed in the thermal magnetic curve at 330 K. Under magnetic fields of 100, 300 and 400 Oe, the magnetization values first increase with increasing temperature, next exhibit a peak and then decrease with further increase in temperature. When the applied magnetic field is sufficiently large, e.g. 1000 and 2100 Oe, the magnetization of the whole sample decreases with increasing temperature. With increasing temperature from the range 77-300 K, the coercivity first increases, next undergoes a peak at about 200 K and then decreases. At room temperature a magnetization jump is observed in the magnetization curves at a field of about 4 kOe in both the aligned and the free powder samples. This jump may be attributed to the spin-flop or metamagnetic transition. The magnetic anisotropy field at room temperature is found to be 8.33 kOe.

Alloys of Sm 10 Fe 90− x Ti x ( x =4.5 and 6) with a stable TbCu 7 -type structure phase and its nitrides have been investigated. The parent compound has planar anisotropy. The nitride has a Curie temperature T c =733 K, anisotropy field μ 0 H a =10.5T and saturation magnetization M S =140J/T kg at room temperature. The room temperature coercivity μ 0i H c reaches 2.3 T and 1.8 T for Sm 10 Fe 85.5 Ti 4.5 N y and Sm 10 Fe 84 Ti 6 N y isotropi c powders, respectively, which were synthesized by high-energy ball milling and nitrogenating.

R3(Fe, Ti)29Cy carbides (R=Nd, Sm) have been synthesized by gas-solid phase reaction. The Curie temperature is enhanced by carbonation, with values of 651 K and 641 K for Nd and Sm carbides respectively. The saturation magnetization of the carbides is slightly lower than that of their parent alloys. The Sm carbide has a large uniaxial anisotropy field, 21 T at 4.2 K and 14 T at 293 K. A coercivity of mu 0iHc=0.3 T at room temperature in the Sm carbide has been developed.

The magnetocrystalline anisotropy of YFe12-xMox and YPe12-xMoxNy (x=1-3, y approximately=1) have been investigated by X-ray diffraction and the singular point detection technique. The uniaxial anisotropy of the YFe12-xMox series decreases with increasing Mox concentration with a clear turning point at about x=1.6. The anisotropy characteristic of the nitride YFe12-xMoxNy changes into a canted-type anisotropy for x or=1.5. The anisotropy reduction for YFe12-xMox is mainly due to the substitution of Mox atoms on the 8i sites, while the further change in anisotropy for YFe12-xMoxNy may be due to a change in the 3d orbital moment or to a change in crystal-field interaction by the interstitial Ny atoms.

In a systematic study of the Sm 10 Fe 85 Ti x (4.7 x 3 (Fe, Ti) 29 compound has been found to be a new phase, of which the structure is Nd 3 (Fe, Ti) 29 -type. The X-ray diffraction pattern of Sm 3 (Fe 0.933Ti 0.06 7) 29 can be indexed on the monoclinic symmetry with the lattice parameters a = 1.065 nm, b = 0.858 nm, c = 0.972 nm and β = 96.98°. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound exhibits ferromagnetic ordering with a Curie temperature T C = 486 K. The saturation magnetization M S is 125 A m 2 /kg at 77 K and 119 A m 2 /kg at room temperature. The room temperature anisotropy field is 3.4 T.

The field dependence of the coercive field for isotropic and aligned Sm2Fe17Nx epoxy resin bonded magnets are investigated. Results indicate that the coercive field of the isotropic magnet is larger than that of the aligned magnet. For small magnetizing fields, the coercive field of the sample magnetized antiparallel to the alignment direction is larger than that of the sample magnetized parallel to the alignment direction of the magnets. When the magnetizing field is large enough, the coercivities obtained after magnetizing the aligned sample in parallel and antiparallel directions are the same. The microstructural parameter derived from the temperature dependence of the coercive field implies that both nucleation and pinning mechanism could be responsible for the magnetic hardening of the Sm2Fe17Nx epoxy resin bonded magnets.

(Sm 1− x Dy x ) 2 Fe 17 C y magnet material with x from 0 to 1 and y ≈ 1.9 was prepared by melt spinning of arc-molten ingots. X-ray diffraction and thermomagnetic scans show that the ingots are basically Th 2 Fe 17 -type structured with low carbon concentration and a large amount of α-Fe. With increasing Dy content there is a tendency for the formation of Sm carbides to be suppressed. After melt spinning the ribbons have a much lower α-Fe content and mostly two phases were found with different Curie temperatures T c in the range up to 400°C. The portion of an amorphous phase increases with the wheel velocity as well as with increasing Sm content. Heat treatment of the melt-spun material results in recrystallization and enhancement of the amount of a Th 2 Fe 17 -type phase with the higher T c value. For annealed material T c increases with the Dy content from about 274°C for x = 0 to 365°C for x = 1. At room temperature the maximum coercivities μ 0 J H c ≈ 0.1 T were found for x = 0 as well as for x = 1. At low temperatures a dip in the demagnetization curves was found for samples with high Dy content ( x ⩾ 0.6). It is supposed that the dip is caused by an easy cone of the magnetization direction at low temperatures.

The magnetic structure of Nd6Fe13 Si has been studied by magnetization measurement, the singular point detection technique and neutron powder diffraction. It was found that the Nd6Fe13Si is ferrimagnetic with a compensation temperature of 357 K and a Curie temperature of 441 K. The spontaneous magnetization values are 12.9 J T-1 kg-1 at 5 K and 7.4 J T-1 kg-1 at 300 K. There are two values B0cr1 and B0cr2 of the magnetic phase transition field below 225 K: B0cr1=6.2 T and B0cr2=8.2 T at 77 K and B0cr=5.3 T at 300 K. The atomic magnetic moments are ordered in an antiparallel manner, and the two magnetosublattices are MI up arrow (8f(Nd), 16l(Nd), 4d(Fe), 16l2(Fe)) and Mn down arrow (16k(Fe), 161(Fe)).

The hard magnetic properties of a new interstitial nitride Sm3(Fe0.933Ti0.067)29Ny (y approximately 5) have been investigated by ball milling. The saturation magnetization linearly decreases with ball-milling time. By ball milling, maxima of remanence Br=1.04 T, intrinsic coercivity mu 0iHc=0.83 T and energy product (BH)max=105 W m-3 are achieved at 293 K.

The isotropic nanostructured iron-rich Fe–Pt films with X Fe =50–73 at% were prepared by annealing DC sputtered Fe/Pt multilayer films. Studies showed that coercivity of these films is mainly controlled by pinning mechanism and magnetization of all films is dominated by ferromagnetic exchange coupling between neighboring grains.

The coercive field of explosion sintered Sm2Fe17Nx magnet is analysed on the basis of micromagnetism. Results indicate that the coercivity of explosion sintered Sm2Fe17Nx magnet is controlled by the nucleation field near the grain surface. The large demagnetization factor originates from the strong strayfields of nonmagnetic poles, magnetically soft phases, and the very sharp corners of Sm2Fe17Nx grains.

Sintered magnets of Sm2Fe17Ny nitrides, with a density of 6.0–7.4 g/cm3, have been prepared by using an explosion technique. Both crystalline structure and the magnetic properties of Sm2Fe17Ny nitrides were retained in the process. The sintered magnet had a remanence Br=0.83 T, an intrinsic coercivity μ0iHc=0.57 T and an energy product (BH)max=88 kJ/m3. The temperature dependence of coercivity and remanence were also measured. The temperature coefficients α of remanence and β of coercivity are −0.076%/°C and −0.51%/°C, respectively.

The Sm2Fe17Ny nitrides with nitrogen concentration y = 2 to 8 have been prepared using a mixed gas atmosphere of NH3 and H-2. Their intrinsic magnetic properties were studied at 1.5 and 293 K. The Th2Zn17-type structure is maintained when y is less than 6. The 9e sites can be fully occupied and the 18g sites may be half occupied by nitrogen atoms. The nitrogen at the 9e sites and 18g sites have a positive effect and a negative effect, respectively, on the intrinsic magnetic properties of Sm2Fe17 compound. The nitride Sm2Fe17N3 has the best intrinsic magnetic properties.

The X-ray diffraction pattern of the novel Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound was indexed on the basis of monoclinic symmetry with the lattice parameters a = 1.065 nm, b = 0.858 nm, c = 0.972 nm and β = 96.98°. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound exhibits ferromagnetic ordering with T C = 486 K and a planar anisotropy. The new interstitial nitride of the Sm 3 (Fe 0.933 Ti 0.067 ) 29 N 5 compound was obtained by gas-solid phase reaction. The nitride has the same structure as the parent compound. The introduction of nitrogen leads to an increase in the Curie temperature to 750 K. The saturation magnetization values σ s = 160 A m 2 kg −1 at 4.2 K and 140 A m 2 kg −1 at 293 K. The anisotropy was changed from planar to uniaxial upon nitrogenation. The anisotropy field B a values were 18.1 T at 4.2 K and 12.8 T at 293 K. The hard magnetic properties of the Sm 3 (Fe 0.933 Ti 0.066 ) 29 N 5 compound have been studied. A coercivity μ 0i H c value of 0.83 T and a maximum energy product ( BH ) max of 105 kJ m −3 at 293 K have been achieved. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 Ny compound is a promising material for permanent magnetic applications.

Two new compounds of the type RFe 11.4 Nb 0.6 (R = Y, Gd) with ThMn 12 structure were synthesized. The corresponding nitrides retain the same structure as their parent alloys, but with an expansion in the unit cell volume of about 3%. The temperature dependences of saturation magnetization and anisotropy field were determined from 4.2 K to room temperature for the Y compound and its nitride. The Curie temperature is 597 K for GdFe 11.4 Nb 0.6 and 773 K for its nitride. The effect of the third stabilizing element on the Curie temperature of ThMn 12 -type ternary rare-earth iron-rich compounds was investigated and discussed in terms of a diagonal positional relationship in the periodic table of the elements.

The structural and magnetic properties of the R(2)Fe(16)SiC(2) (R = Y, Sm, Gd, Tb, Dy, Ho, Er and Tm) compounds have been investigated. These carbides were prepared by the arc-melting method and found to crystallize in the rhombohedral Th2Zn17-type structure. The substitution of Si for Fe in the R(2)Fe(17)C(2) compounds is able to stabilize the structure of the 2:17-type carbides although it results in small decreases in saturation magnetization and Curie temperature. The Sm2Fe16SiC2 compound is found to have a uniaxial magnetocrystalline anisotropy and shows a roam-temperature anisotropy field of about 110 kOe. Spin-reorientation transitions are observed in the Er2Fe16SiC2 and Tm2Fe16SiC2 compounds. The replacement of Fe by Si in the R(2)Fe(17)C(2) compounds increases the uniaxial anisotropy of the R sublattice, resulting in the increase in spin-reorientation temperature.