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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.

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 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 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 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.

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.

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.

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.

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.

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 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.

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.

The interstitial carbides R2Fe17Cx (x∼2) have been prepared by gas-phase modification with acetylene for R = Y, Sm and Er. The average iron magnetic moments derived from the magnetizations of Y2Fe17Cx at temperatures of 1.5 K and 293 K respectively are 34.1 μB/f.u. and 28.9 μB/f.u.. The anisotropy fields of Sm2Fe17Cx at T = 1.5 K and 293 K are respectively 21.7 T and 13.5 T. A spin reorientation transition was observed at 124 K for Er2Fe17Cx.

57Fe Mossbauer spectra of an oriented absorber of Sm2Fe17 were studied in the temperature range 15–290 K. The isomer shifts decrease with temperature and the 6c site has a shift which is 0.2 mm s−1 greater than the other three iron sites. The quadrupole splitting hardly changes with temperature for all four sites. The hyperfine fields for each Fe site decrease smoothly with temperature without any anomaly. Average values are 30.1 T and 22.1 T at 15 K and 290 K respectively. The data indicate that the easy magnetization direction is along a b-axis over the whole temperature range. There is no spin reorientation of the magnetization to the c-axis.

57Fe Mossbauer spectra have been obtained at room temperature and at 15 K for R2Fe17 and R2Fe17N3- delta ( delta approximately=0.4) with R identical to Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y. The easy direction of magnetization of the R2Fe17 compounds can be identified by analysis of the hyperfine field and quadrupole interactions. For rare-earth elements with J>3, the sixth-order crystal-field parameter B66 determines the easy magnetization direction in the basal plane. In the nitrides, the average hyperfine field at 15 K increases by approximately 13% above the value in the parent compounds, from about 31 to 35 T, and it is anisotropic, being greatest when the magnetization lies along the c-axis. There is also an increase in the isomer shift of 0.12(2) mm s-1. Spin reorientation transitions occur in the nitrides of Er and Tm; only the samarium nitride has an easy c-axis at room temperature, but Sm, Er and Tm all have easy c-axis magnetic structures at 15 K.

In the present paper, a study of the effect of the volume change on the Curie temperature of R–Fe–N and R–Fe–Ti–N compounds with TbCu 7 structure has been performed. Our results indicate that the relationship between dln T C /dln V and the Curie temperature T C in rare earth –iron based nitrides with TbCu 7 structure can be well described in terms of the itinerant-electron model formalism.

In the present work, the phenomenon of simultaneous enhancement of remanence and coercivity for Nd–Fe–B/Nb magnets prepared by sintering of mixed Nd–Fe–B and Nb powders is reported and its mechanism is investigated. The appropriate addition of Nb powder may suppress the appearance of Nd-rich phases at Nd 2 Fe 14 B grain boundaries and the excess Nd-rich composition may become available to form more of the Nd 2 Fe 14 B phase, which is responsible for the enhancement of the remanence. The reversal of hard Nd 2 Fe 14 B grains was suppressed by a decreasing amount of α-Fe, by better decoupling between the magnetic grains due to formation of the Nb-rich phase or by pinning of domains at the Nb-rich phase.

Spin reorientations from the c-axis at low temperatures to the c-plane at higher temperatures are observed at 120 K in Er 2 Fe 17 N 2.7 and at 200 K in Tm 2 Fe 17 N 2.7 . The corresponding crystal field parameters B 20 are -0.117(12) K/ion and -0.357(35) K/ion espectively, and the average effective crystal field coefficient A 20 is -59(7) Ka 0 -2 . Implications for the anisotropy of Sm 2 Fe 17 N 3−δ are discussed.

The Curie temperature of Y2Fe17Cx increases linearly with carbon content in the hexagonal phase, 0 ⩽ × ⩽ 1. It saturates at 520 K for x ⩾ 1.1, where the phase becomes rhombohedral. The iron moment and magnetization for Y2Fe17C at T = 0 K and 290 K respectively are 2.08 microB and 1.56 T, 1.65 microB and 1.25 T. Thermopiezic analysis shows that the carbide absorbs hydrogen at 250 °C at 1 bar. Hydrogenated carbides show a further increase in Tc.

In the present work, hard magnetic behaviours of (Sm1-yPry)2Fe17Nx magnets are investigated. Remanence enhancement is observed when some of the Sm atoms are replaced by Pr atoms in the compounds, which is due to the larger saturation magnetization of (Sm1-yPry)2Fe17Nx than of pure Sm2Fe17Nx. Meanwhile the coercivity of (Sm1-yPry)2Fe17Nx decreases with increasing Pr content in the compounds, which corresponds to the decrease of the anisotropy field in the compounds. In order to obtain a combined good effect on the remanence and the coercivity, the Pr content y should be no more than 0.4 in (Sm1-yPry)2Fe17Nx nitrides.

New members of ThMn/sub 12/-structure family RFe/sub 11.35/Nb/sub 0.65/ (R=Y, Dy, Er) have been synthesized and studied by x-ray diffraction, ac susceptibility measurements and thermomagnetic analysis. Spin reorientation transitions were observed in DyFe/sub 11.35/Nb/sub 0.65/ and ErFe/sub 11.35/Nb/sub 0.65/ compounds. The transition temperatures of spin reorientation were determined to be T/sub sr1/=160 K and T/sub sr2/=235 K for DyFe/sub 11.35/Nb/sub 0.65/, and T/sub sr/=41 K for ErFe/sub 11.35/Nb/sub 0.65/, respectively. The spin reorientation transitions are quenched by nitrogenation. >

The formation, structure and magnetic properties of (Er1-xYx)(2)Fe17C2 (0 less than or equal to x less than or equal to 1.0) prepared by melt spinning were studied. Arc-melted (Er1-xYx)(2)Fe17C2 alloys are found to have a two-phase structure with the 2:17 phase and a predominant alpha-Fe phase. Melt spinning (ER(1-x)Y(x))(2)Fe17C2 results in the crystallization of the Th2Zn17-type structure at appropriate quenching rates of v(s)=10-20 m s(-1). X-ray diffraction and thermomagnetic measurements show that they are of single phase. The substitution of Y for Er was found to have a small influence on the unit-cell volume v and Curie temperature T-c. The saturation magnetization sigma(s) is enhanced from 77.4 to 169.0 emu g(-1), as x increases from 0 to 1.0, but the Fe magnetic moment is approximately constant. Spin reorientation transitions are observed in the samples with x less than or equal to 0.8. The substitution of Y decreases the uniaxial anisotropy of the Er sublattice, resulting in a monotonic decrease in spin reorientation temperature from 137 K for x=0 to 44 K for x=0.8.

In the present work, the diffusion mechanism of gas atom (C, N) into Sm2Fe17 lattice has been investigated. Results indicate that gas atoms (C, N) under different states of gas absorption content x in Sm(2)Fe(17)Z(x) (Z=C, N) are of different diffusive activity due to the interaction strength between gas atom and interstitial site of Sm2Fe17 molecule. In the region of x x(0), such interaction is small and part of nitrogen atom with amount of Delta x=x-x(0), in Sm(2)Fe(17)Z(x) are active for further diffusion and can migrate easily in Sm2Fe17 lattice.

The crystal and magnetic structure of Nd2Fe17N4.5 at room temperature was refined by Rietveld analysis of neutron-powder-diffraction data. We found that Nd2Fe17N4.5 has a Th2Zn17-type structure (space group R 3m) and the nitrogen atoms occupy both 9e and 18g sites with occupancies 0.80 and 0.35, respectively. A physical model is proposed based on the large isotropic thermal factor for the 18g sites.

On montre que le compose Sm(Fe 11 Ti) presente une variation discontinue de son aimantation quand un champ de 9T est applique a basse temperature perpendiculairement a l'axe c. On propose un modele prenant en compte un melange des multiplets J pour expliquer ces observations

Etude de trois series de compositions ternaires, R 2 M 3 Fe 21 , YM 3 Fe 9 et Y 2 M 3 Fe 8 (M=Zr, Sc)

Magnetic properties of the series of ThMn12-structure intermetallic compounds R(Fe11Ti) have been determined for rare earths from Nd to Lu plus Y. The highest Curie temperature (607 K) is for R=Gd, and R-Fe exchange interactions are much stronger for light rare earths than for heavy ones. The temperature dependence of the iron sublattice magnetisation and anisotropy are determined for the Y and Lu compounds. Spin reorientation transitions are found as a function of temperature for the rare earths with a negative second-order Stevens coefficient alpha J(Nd, Tb, Dy), and a set of crystal-field parameters is derived to account for the transitions in a consistent way. A sharp increase in magnetisation observed for Sm(Fe11Ti) below 130 K in a field of about 10 T applied perpendicular to the easy direction indicates that J-mixing may be important for Sm3+. Compared with R2Fe14B, the iron anisotropy in R(Fe11Ti) is greater, and the rare-earth anisotropy is much weaker at low temperature, with the opposite sign for the rare-earth crystal-field coefficient A20. The average iron moment is 1.7 mu B in R(Fe11Ti) at 4.2 K; Mossbauer spectra are analysed to yield the average moments on each site. Limits set by the intrinsic magnetic properties on the performance of magnets made from these families of alloys are discussed.

Spin reorientation transitions to a ground state where the magnetization is not parallel to c-axis, are observed below room temperature in R(Fe 10 V 2 ), R = Nd , Dy , Ho and Er . These are quantitatively explained by using a set of five crystal-field coefficientsd derived from the fit of the magnetization curves of a Dy(?Fe 11 Ti) crystal. An explanation is given of why first-order spin reorientation transitions are found in Ho(fe 10 V 2 ) and Ho(Fe 10 No 2 ), but not in Ho(Fe 11 Ti).