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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.

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.

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 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, 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.

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.

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.

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.

The enhancement of room temperature magnetoresistance can be induced by the Ti substitution for Mn in La 0.67 Sr 0.33 Mn 1− x Ti x O 3 , which may be connected with the shift of the Curie temperature from a high temperature to the near room temperature by the Ti substitution. This experimental observation may provide a route to improve CMR behavior of the perovskite manganites at room temperature.

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.

In the present work, the structure, magnetic properties and magnetoresistance effect of Ni1−xMnxFe2O4 (x=0,0.2,0.4,0.8) sintered ferrites are studied. Results indicate that these ferrites crystallize in the cubic spinel structure. Curie temperature decreases but the saturation magnetization increases with increasing Mn content in Ni1−xMnxFe2O4 sintered ferrites. A large magnetoresistance effect has been found in samples x=0.4 and x=0.8.

In recent years, there has been much interest in the perovskite compounds R1−x Ax MnO3 (R=La, Pr and A= Pb, Ca, Sr, Ba) with a Mn3+/Mn4+ mixed valence [1–13]. In the doping range 0.2< x < 0.5, these manganites undergo a paramagnetic insulator to ferromagnetic metal phase transition upon cooling, leading to a sharp resistance peak near the Curie temperature TC. Application of an external magnetic field of few teslas suppresses the resistance greatly. Within the double– exchange interaction model the itinerant carriers in the substituted R1−x Ax MnO3 oxide provide the mechanism for ferromagnetic interaction between Mn3+ and Mn4+ ions. The ferromagnetic Curie temperature is related to the strength of the transfer intergral ti j between Mn3+ and Mn4+ ions which control the the electronic (hole) conductivity. The unusual temperature and magnetic field dependent resistance exhibited by these compounds reflects a novel interplay between magnetism and electronic transport. It has been shown recently that the substitution of Mn3+ by Co3+, Ni3+, Cr3+ in R0.5A0.5MnO3 destroys the charge–ordered state and renders the material ferromagnetic and metallic when the average size of A–site cation, 〈rA〉, is larger than 1.17 A [10–12]. In the present work, we report the effects of the Ni-doping on the perovskite compound La0.67Ca0.33MnO3. Samples La0.67Ca0.33Mn1−x Nix O3 (x = 0, 0.05, 0.1 and 0.2) were prepared using solid state reaction method. Mixed powders of La2O3, MnO2, Ni2O3 and CaCO3 were ground for 60 min, then ball-milled for 30 min and pressed into flats. The flats were first heated at 800 ◦C for 24 h and subsequently pulverized. After being milled for 30 min, they were pressed into flats again, then sintered at 1300 ◦C for 100 h, followed by furnace–cooling in the atmosphere. X-ray diffraction analysis by Cu-Kα radiation was used to confirm a single phase with perovskite structure. The thermal– magnetic analysis using a vibrating sample magnetometer (VSM) at a small field of 0.04 T was performed from 77 to 300 K. The resistance were measured by a standard four–terminal method. The magnetization curves and magnetoresistances at 5 K, and the temperature dependence of the resistance at both zero field and H = 6 T from 5 to 300 K were determined using a superconducting quantum interference device (SQUID) magnetometer.

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 a systematic study of the ternary iron-rich rare earth alloys GdFe12−xGex (3.6 < x < 8.0), a new ternary iron-rich rare earth intermetallic compound of the approximate composition GdFe8.4Ge3.6 has been synthesized. The Curie temperature of the compound GdFe8.4Ge3.6 is about 928 K. The lattice symmetry of the compound is tetragonal. The light rare earth compound SmFe8.4Ge3.6 was also prepared, and its lattice parameters and Curie temperature are reported.

The impedance as well as the resistance and reactance of the La0.75Sr0.25MnO3 manganite increase with increasing ac frequency due to the skin effect of the metal state below Curie temperature. The manganite La0.75Sr0.25MnO3 shows not only the colossal magnetoresistance effect but also the giant magnetoimpedance effect. For the giant magnetoimpedance, the magnetic field influences the impedance by affecting the penetration depth via the transverse permeability, whereas for the colossal magnetoresistance the magnetic field tends to align the local spins, leading to the decrease of the dc resistance via the interplay between a strong electron–phonon coupling and the double exchange effect of spin alignment on electron kinetic energy.

The structure and magnetic properties of RTi 1.1 Fe 10.9 alloys were investigated. X-ray analysis of the compounds revealed that RTi 1.1 Fe 10.9 alloys are of the tetragonal ThMn 12 structure. The lattice constants of these compounds were determined. The Curie temperature, the saturation magnetization at 1.5 and 300 K and the magnetic anisotropy fields at 77 and 300 K for RTi 1.1 Fe 10.9 were determined. The temperature dependences of the magnetization in the range of 1.5–300 K were measured for SmTi 1.1 Fe 10.9 and HoTi 1.1 Fe 10.9 . We found that R-Fe exchange interaction is ferromagnetic for light R and ferrimagnetic for heavy R. At 77 and 300 K, the compound RTi 1.1 Fe 10.9 (R = Sm, Y, Gd, Er, Ho) has an easy axis but it seems that TbTi 1.1 Fe 10.9 has an easy plane. The spin reorientation from planarto axial was observed for DyTi 1.1 Fe 10.9 at about 185 K. At the same time we found the FOMP for SmTi 1.1 Fe 10.9 , HoTi 1.1 Fe 10.9 and ErTi 1.1 Fe 10.9 . The initial critical field of FOMP at 77 K was determined.

The structure and magnetocrystalline anisotropy of SmMo2Fe10 alloy were investigated. X-ray analysis revealed that SmMo2Fe10 has the tetragonal ThMn12 structure with parameters a = 8.6015 A , c = 4.7996 A , v = 355 A 3 . SmMo2Fe10 has an easy axis [001] from 78 to 293 k. The temperature dependence of the magnetization was measured. The Curie temperature was found to be 463 K. The temperature dependence of magnetic anisotropy field in the range 77 k – 300 k was determined. The value of magnetic anisotropy field at 300k is 45 kOe. It shows that SmMo2Fe10 based alloys can serve as permanent magnet materials.

Permanent magnets in the Nd16.5(Fe1−xCox)76.5B7 system were prepared by powder metallurgical methods. Magnetic hysteresis loops, with the magnetic field parallel and perpendicular to the aligning direction, were measured in the temperature range from 4.2 to 450 K. The magnetic anisotropy constants K1 and K2 of Nd2(Fe1−xCox)14B with 0≤x≤0.4 were determined by using aligned sintered magnets Nd16.5(Fe1‐xCox)76.5B7. The intrinsic coercive force iHc, magnetic anisotropy constants K1 and K2, and spin reorientation temperature decrease monotonically with increasing Co concentration.

The composition dependence of Curie temperature, spin reorientation temperature and magnetic anisotropy field are investigated for Nd2 (Fe1-xTx)14B (T = Nb, Mo and Ga) alloys. The contribution of pinning to the magnetic hardening for NdFeNbB sintered magnets increases with the Nb addition. Precipitation has been found in NdFeNbB sintered magnet.

Sintered magnets (Nd1−xDyx)16.5(Fe0.85Co0.15)76.5B7 with 0≤x≤0.2 were prepared. In the temperature range 4.2–450 K, the magnetic hysteresis loops with parallel and perpendicular to aligned directions were measured applying a field up to 15 T. The temperature dependence of the permanent magnetic parameters for the magnets with various Dy concentrations was shown. Using a modified Sucksmith‐Thompson plot, the magnetic anisotropy fields of (Nd1−xDyx)2(Fe0.85Co0.15)14B were determined from the experimental results of sintered magnets. As Dy concentration increases, the anisotropy field of the magnets apparently increases, while the anisotropy field of the magnets decreases linearly. Substituting Dy for Nd, there is no effect on Curie temperature of the magnets, which was determined from that of SmCo‐type magnets, there exists a transition from nucleation dominated at a low magnetizing field to pinning dominated at a high magnetizing field.