A model for disaccommodation in single crystals of yttrium iron garnet (YIG) irradiated with white light is proposed. Only oxygen vacancies are considered to be the origin of triple peaks of disaccommodation, DA, around 130K (DA(I)), 200K (DA(II)) and 300K (DA(III)). Taking account of the number of electrons trapped in oxygen vacancy, mechanisms of DA in the three divisions are explained. The model is confirmed by the irradiation dependence of DA and the thermal hysteresis of DA(I) and DA(II).

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Optical and magneto-optical spectra of the insulating granular system Co-Al-O prepared by reactive sputtering are measured in the energy range 0.5-3.8 eV. The trans- verse Kerr effect magnitude in the Co₅₂Al₂₀O₂₈ film attain large values. The data have been interpreted in the frame- work of the effective medium approximations: Bruggeman (BA) and symmetrised Maxwell- Garnett approximation (SMG). The best fit between experimental data and theoretical prediction was obtained in SMG. It is shown that magneto-optical spectra of ferromagnetic composites are highly sensitive to composite microstructure.

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We develop the symmetrised Maxwell-Garnett (SMG) approximation for magneto-optical spectra calculations by introducing an average over two following random units: inclusion of A coated by shell of B and inclusion of B coated by shell of A. Thus the symmetrised Maxwell-Garnett approach is the modified version of both Maxwell-Garnett and Bruggeman theories for arbitrary values of ferromagnetic volume fraction. The calculated spectra of metal-metal granular alloys in Bruggeman and SMG approaches are closed to each other, but this is not the case for metal-insulator composites, especially when close to percolation threshold. It is shown that magneto-optical response of the ferromagnetic composites is extremely sensitive to the value of the percolation threshold and hence to the microstructures of the composites.

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Based on experimental results of high temperature thermal expansion, paramagnetic neutron scattering, considerations of the relative stability of the various phases of elemental Fe and total energy calculations, we discuss the interrelated aspects of Invar, anti-Invar and martensitic phase transformations in Fe-rich alloys. The physical background to the discussions is provided by ab initio calculations of the magnetic and structural binding surfaces of pure Fe and Fe- based alloys. Decisive are charge transfers between electronic levels with different symmetry (e_g and t_2g) and their non-bonding and anti-bonding character. The variation with composition of the size of the Invar and anti-Invar effects is a question of the position of the Fermi energy relative to these levels. How an effect manifests itself as a function of temperature is a question of the energetic difference between these levels.

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By meclianically alloying and successive heat treatment, Fe-Ni Invar alloys around 35 at% Ni have been made with wide variety of concentration fluctuation. Observed magnetization curve changed significantly by annealing. The saturation magnetization decreased first, took a minimum at 500°C annealing and then increased further increasing annealing temperature. By assuming Gaussian-type fluctuation, observed magnetization curves could be explained.

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Magnetostriction has been measured on commercial plycrystalline Fe+27%Co from room temperature to about 600°C using unbonded strain gages and a high- temperature mounting cement. The gage is excited at 1 kHz, and the sample driven around its hysteresis loop to a maximum field of about 200 Oe in a tune less than 15 seconds to minimize the strain due to temperature drift. Room temperature magnetostriction values agree reasonably well with those quoted by Bozorth (30 to 40 microstrain), and remain almost constant up to at least 350°C and sometimes higher, depending on the heat treatment of the sample. It therefore seems clear that stress-magnetostriction anisotropy will be significant in these alloys at high temperatures.

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We have systematically investigated the effect of microstructure on the magnetic properties of Fe_balCo₄₉V_1.9, Fe_balCo₄₉V_1.9Nb_0.3, Fe_balCo₂₇Cr_0.6Ni_0.6, Fe_balCo₂₇Cr_0.6Ni_0.6C_0.3 alloys in a temperature range of 20-700 °C. The effects of microstructure, the grain size, second phase precipitation, density of dislocation, and structural ordering parameter have been separated each other and been determined. The second phase precipitation which appears in high temperature aged samples causes the magnetic properties to deteriorate significantly. The increase of the structural ordering parameter, which was determined by neutron diffraction, improves the magnetic properties. The grain size mainly affects the coercivity field.

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Rapid-solidified, melt-spun ferromagnetic shape memory Fe-29.6at%Pd alloy was fabricated to develop a new type of magnetostrictive material. The thin plate samples showed stronger crystal anisotropy and larger shape memory effect. Magnetostriction changed with increasing temperature up to 1750 microstrain at H= 10kOe just below the inverse phase transformation temperature. This phenomenon might be caused by the magnetically induced re-arrangements of the activated martensitic twin variants. The basic mechanism of this giant magnetostriction and its dependency on metallurgical microstructures are discussed.

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The magnetostatic critical point phenomena of a single crystalline Ni (fcc) were first investigated using a computer controlled vibrating sample magnetometer in the uniformly applied bipolar fields from 0 to ±8 kOe. The magnetization M was measured along both of the easy axis [111] and hard axis [100]. A clear kink point locus was observed for the whole critical region in the extremely low fields measurement and the spontaneous magnetization and the critical point were directly obtained without data reduction for both easy and hard axes. The critical indices for the easy axis and hard axis were obtained to be β=0.385 ±0.002 and 0.426±0.003, γ =1.302±0.003 and 1.19±0.01, and δ=4.27±0.01 and 3.80±0.01, respectively. The effect of the magnetocrystalline anisotropy on the critical indices is first found to be significantly large and not negligible in Ni. It was clearly shown that the Griffith's inequality is valid and the scaling low for the critical indices fails, and that all of the measured data for easy axis support the existence of the equation of statesΨ(H, M) but does not for the low field data at hard axis.

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Thermal expansion of α-Mn has been measured at high pressures up to 2.2 GPa in order to examine the relation between the instability of antiferromagnetism and the magnetovolume effect. It is found that T_N goes down and the magnitude of spontaneous volume magnetostriction becomes small as pressure increases. The antiferromagnetism of α-Mn is suggested as disappearing below 5 GPa.

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Using the self-consistent tight-binding-linear-muffin-tin-orbital (TB-LMTO) recursion method, we have investigated the rearrangement of electronic structures with the addition of both s, p-element (Al, Si, and P) and 3d-element impurities in bcc ferromagnetic Fe. We have obtained local density of states (LDOS), charge transfers, and magnetic moments. In the case of s, p-element impurities, we have found that the s-level LDOS at the impurity site has a dip in the vicinity of the bare d-level of the host, which is related to the Fano anti-resonance. We have also found that the simple dilution model for the impurity works well for Al, Si, and P impurity in Fe. As for transition metal (TM) impurities, we have found that early TM impurities (Ti-Cr) favor antiferromagnetic arrangements with respect to the host Fe spins, while late TM impurities (Mn-Ni) favor ferromagnetic arrangements.

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A new method to estimate the coercivities of transition metal magnetic systems is proposed within the framework of itinerant-electron magnetism. By studying the transverse magnetic susceptibility under a Hartree-Fock approximation, the dispersion relations of the spin wave excitations are obtained, which possess positive gap induced by the anisotropiclly-coupled spin-orbit interactions if the magnetization is in its easy axis. When a magnetic field is applied opposite to the spontaneous magnetization and if it is strong enough to overcome the excitation gap, a spin reversal transition will take place which defines the coercive field. Applications are given to some small magnetic microclusters.

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Stoichiometric Ni₂MnGa has a Heusler-type crystal structure and is ferromagnetic. The specimens of stoichiometric and nonstoichiometric Ni₂MnGa were made by arc melt method. The phase transformation temperature and the Curie temperature of these alloys were determined by the results of a differential scanning calorimeter and A. C. magnetic permeability measurement. The phase transformation temperature increased and the Curie temperature decreased with increasing Ni composition. The phase transformation coincided with the Curie temperature in Ni_2.18Mn_0.82Ga.

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NMR spectra of ⁵⁵Mn and ⁵⁹Co in MnCoGe with two different structures have been measured in zero field at 4.2 K. In MnCoGe with an orthorhombic structure the peak frequencies of ⁵⁹Co and ⁵⁵Mn resonances are observed at 180 MHz and 350 MHz, respectively. In MnCoGe with a hexagonal structure those are observed at 143 MHz and 287 MHz. The Mn magnetic moments of MnCoGe with the orthorhombic structure is found to be larger than that of MnCoGe with the hexagonal structure.

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The electrical resistivity and the thermoelectric power of Mn_3-xFe_xGaC (x≤0.1) are measured. The magnetic phase diagram of Mn_3-xFe_xGaC is determined from the results of these measurements. With increasing iron concentration x, an intermediate magnetic phase(I) appears between the antiferromagnetic(AF) phase and the ferromagnetic(F) one . The AF-I transition temperature T_t1 and the I-F transition one T_t2 decrease with increasing the concentration x.

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The magnetic state of FeRh_1-xPd_x alloys was investigated under pulsed magnetic fields up to 400 kOe. The FeRh_1-xPd_x alloys with the body-centered tetragonal (bct) structure exhibit three kinds of the magnetic phase transition with increasing temperature, depending on Pd composition: the antiferromagnetic(AF) -paramagnetic(PM) transition at the Néel temperature (0.25<x<0.53), the ferromagnetic(FM)-PM transition at the Curie temperature (0.61<x<1.0), and the AF-FM-PM transition (0.53<x<0.61). The triple point is x=0.53 and T=370K. It was found that the FM state was induced from AF state by the application of high magnetic field. The critical field varies from 30 kOe to the field higher than 100 kOe with varying Pd composition. Interestingly, the induced ferromagnetic phase of FeRh_1-xPd_x is different from that of equiatomic FeRh alloy in remaining even after decreasing fields to zero.

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The anisotropic magnetomistance AMR of fcc FeCoNi alloys was measured using single crystals to investigate its mechanism and to make clear the relation between AMR and magnetostriction. AMR tensor components k₁ and k₂ were evaluated. The maximum of k₁ (∼(Δρ/ρ)_I//[001]) and the minimum of k₂(∼(Δρ/ρ)_I//[111]) at 10K are about 68% and -32%, respectively, both of which are observed around Ni₈₀Co₂₀. The value of k₁ exhibits a maximum at the mean electron number per atom e/a ∼27.8 and shows a small hump at e/a ∼26.8. At these e/a values, the magnetostriction constant λ₁₀₀ becomes zero. The relation between AMR and magnetostriction is discussed.

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The de Haas-van Alphen (dHvA) effect was measured for the paramagnetic compound CrP with an orthorhombic MnP-type structure using a high quality single crystal. Ten branches of dHvA frequency below 9200T are obtained in the (010) plane at 0.6K. Four frequencies in a field along the symmetry axes agree qualitatively with the theoretical results calculated with an all-electron relativistic LAPW method. The cyclotron mass ratios in two branches along the [100] axis are 4.6 and 3.1, respectively.

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NMR properties of ³¹P in CrRuP at low temperatures are reported. The compound CrRuP, which is a member of a series of compounds MRuP (M=3d transition metal), was expected to be in a nonmagnetic state at low temperature such as a Kondo insulator from the susceptibility data. However, field-swept and zero-field NMR spectra show that it is an antiferromagnet at low temperature. The hyperfine field at the ³¹P site at 4.2 K is determined to be 9.6 kOe with a half-width of 2.3 kOe. A simulation using the broad zero-field data and a simple antiferromagnetic spin structure explains the field-swept powder spectrum only qualitatively, suggesting a complex antiferromagnetic spin structure in this material.

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The magnetization curves of TiBe₂ were measured up to 90 kOe at temperatures 0.55 ∼30.1 K. An abrupt increase of the magnetization was observed at about 50 kOe, but is not a first-order transition down to 0.55 K. We estimated the non-linear susceptibility χ₃(T), which is related to the amplitude of paramagnetic spin fluctuations, is positive below 15 K and decreases with increasing temperature. Moreover, it is confirmed that the temperature for χ₃(T) =0 is close to that at which the linear susceptibility becomes maximum. These features are expected by a spin fluctuation theory of itinerant electron metamagnetism.

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Specific heat was measured as a function of temperature for RNi compounds (R : heavy rare earth). It was found that the large magnetic contributions to the observed specific heat still remains far above T_c, which is well explained by the Schottky type anomaly.

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Itinerant-electron magnetic properties of LU(Co_0.90Al_0.10)₂ Laves phase intermetallic compound under high pressures up to 1.0 GPa have been investigated. The compound has a critical concentration of the onset of ferromagnetism. The spontaneous magnetization decreases with increasing pressure and disappears above 0.6 GPa. In the paramagnetic state induced by applying pressure, a metamagnetic transition from a paramagnetic to ferromagnetic state occurs in magnetic fields. An anomalously large negative pressure dependence of the Curie temperature has been observed, which is explained by the Landau expansion of free energy taking spin fluctuations into consideration.

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The high-field magnetizations of Y(Co_1-xAl_x)₂H_y have been measured for 0≤x≤0.075 and 0≤y≤3.44 in pulsed high magnetic fields up to 42 T. The itinerant metamagnetic transition is broadened, but clearly observed in Y(Co_0.925Al_0.075)₂H_y with y≤0.72. The value of the critical field B_c of the transition decreases nearly linearly with increasing hydrogen content in the region y<0.28, which is consistent with the decrease of the transition field due to Al substitution for Co in the parent compound. A weak spontaneous moment appears in all the hydrides, which originates from a partial structural disordering of the lattice induced by hydrogen absorption.

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Thermal expansion of ErCo₂; has been measured at high pressures up to 2 GPa. It is found that T_c goes down and the magnitude of spontaneous volume magnetostriction becomes small as pressure increases. The origins of pressure change of T_c and spontaneous volume magnetostriction are discussed briefly in connection with the induced moment on Co atom.

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Giant magnetostriction (GMS) of Tb_0.3Dy_0.7Fe_1.9 single crystal has been measured at hydrostatic pressure up to 9 kbar. The electrical resistance and thermal expansion were also measured at low temperature down to 4.2 K to examine low temperature behavior. It is found that the magnitude of GMS increases with increasing pressure below 4 kbar but decreases above 6 kbar having a maximum near 5 kbar. The origin of maximum is discussed briefly the difference between hydrostatic pressure and uniaxial pressure is pointed out.

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The spin-reorientation transition from [111] to [100] easy axes in Tb_xDy_1-xFe₂ for 0.29<x<0.395 has been studied by X-ray diffraction and a. c. susceptibility measurements. It was determined from the type of the magnetoelastic lattice distortion that the spin-reorientation occurs through an angular <uuv>-type phase in annealed samples, whereas as-cast samples show the transition through a mixture of <100> and <111> phases. After annealing the transition temperature lowered by 10-20 degrees.

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A system of SmFe_12-xNb_x compounds has been synthesised. Both x-ray diffraction patterns and thermomagnetic analyses show that the compounds investigated are almost of single phase and crystallise in the ThMn₁₂-type structure. X-ray diffraction patterns of magnetically-aligned powder samples indicate that the easy magnetization direction at room temperature of these compounds is along c-axis. The effects of Nb content on magnetic properties, such as magnetocrystalline anisotropy fields, the Curie temperatures and saturation magnetizations, have been investigated.

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Structural and magnetic properties of the Y(Fe_1-xCo_x)₁₁Ti compounds have been investigated. Substitution of Co for Fe does not change the crystal structure, but leads to a decrease of unit-cell volume. The Cure temperatures T_c increase clearly with increasing Co content. Composition dependence of the Curie temperature has been studied in terms of the mean field theory. X-ray diffraction spectra measurement has been used to determine the easy magnetization direction(EMD) at room temperature. The magnetocrystallline anisotropy fields have been obtained by use of singular point detection(SPD) technique. The effects of substitution of Co for Fe on magnetic moments have been analysed.

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The magnetic properties of YFe_12-xMo_x alloys (x=1-3) have been studied by ac susceptibility χ_ac , low field thermomagnetic analysis (TMA) and an extracting sample magnetometer in a temperature range of 1.5-300K. Data from χ_ac and TMA indicate that there is a magnetic phase transition occurring below 200K for the alloys with high molybdenum concentrations. The magnetic transition temperature T_f increases as the molybdenum concentration increases. At room temperature, the YFe_12-xMo_x alloys have a hard ferromagnetic phase with uniaxial magnetocrystalline anisotropy. But below T_f, high molybdenum alloys exhibit mectomagnetic behaviour and show obvious magnetohistory effects and a large coercivity, e.g., about 1.7 Tesla for YFe_9.5Mo_2.5 at 1.5 K.

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We performed high-field magnetization measurements for the aligned powder of a high-quality Sm₂Fe₁₇N_3.1 at 4.2 K up to 23 T. The result indicates a strong anisotropic behavior in the magnetization curves along the parallel and perpendicular directions to the aligned one. From the hard axis-magnetization curve, the uniaxial anisotropy constants K₁ and K₂ in the expression as E_a=K₁sin²θ+K₂sin⁴θ were estimated to be K₁=2.3 x10³J/kg andK₂=2.5 x10³ J/kg using Sucksmith-Thompson plot. These values are the largest among the previously reported ones. Assuming that the J-mixing is neglected at zero temrerature, the crystal electric field parameter A₂⁰ estimated from K₁ and K₂ is ∼ -650 K/ a₀², the value of which fairly agree with the theoretically estimated value.

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Neutron powder diffraction (10∼300K) and powder X-ray diffraction (17∼840K) studies were carried out on rhombohedral Y₂Fe₁₇ and Y₂Fe₁₇N_3.1. The interatomic distance between Fe(c)-Fe(c) (dumbbell pairs) was found not to change with temperature in the range from 10 K to 300 K. Nevertheless, a large spontaneous magnetostriction was observed in the c parameter of Y₂Fe₁₇. This suggests that the large spontaneous magnetostriction in Y₂Fe₁₇ is caused by distorting so as to minimize the whole magnetic interaction energies in an itinerant 3d electron system, but not by lowering the locally negative interaction energies in the dumbbell pairs. However, by nitrogenation, the large spontaneous magnetostriction was suppressed, which suggests that the band structure changed from weak ferromangnetic to strong ferromagnetic state.

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Magnetization measurements have been performed for Ce₂F₁₇ under high pressure up to P=1.2 GPa and high magnetic fields up to 17 T. At P=0 GPa, two antiferromagnetic phases appear at T_N=215 K and T_c=125 K with decreasing temperature. A metamagnetic transition from the antiferromagnetic to the forced ferromagnetic state is observed at low temperatures. The transition field increases with increasing pressure, whereas the saturation magnetization, saturation field and T_N decrease. New magnetic phases, which are different from the two antiferromagnetic and forced ferromagnetic phases, are observed under high pressure and high magnetic fields.

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Thermal expansion coefficients of polycrystalline CeRh₂Si₂ under high pressure up to 2.15 GPa have been measured in the temperature range from 5 to 300 K. It is found that the antiferromagnetic ordering temperature T_Nl and the magnetic order-order transition temperature T_N2 decrease with increasing pressure and the antiferromagnetism disappears at high pressure. A positive spontaneous magnetostriction, of the order of 10^-4, is observed below T_N1, which also disappears above P_c = 1.11 GPa. The results are explained qualitatively by the competition between the Kondo and the RKKY interactions. Similarity between the present P-T phase diagram and the Doniach's one is pointed out.

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We performed the measurements of magnetization of the pseudo ternaries Gd_1-xLa_xMn₂Ge₂ with 0≤x≤0.2 in the temperature range from 4.2K to 480K in magnetic fields up to 6T. For x=0.05 and 0.06, the system shows the ferrimagnetism at high temperatures, it transforms to the antiferromagnetism at an intermediate temperature with decreasing temperature, and finally indicates a reentrant ferrimagnetism like SmMn₂Ge₂. For x≥0.1, the system exhibits the ferrimagnetism in all ordering temperature range, accompanied by a compensation phenomenon. The compensation behavior as a function of temperature is discussed on the basis of two sublattice molecular-field model.

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The structural and magnetic properties of crystalline and amorphous alloys of La(Co _1-xMn_x) ₁₃ have been investigated by X-ray diffraction and magnetization measurements. The structure of amorphous alloys consists of the icosahedral clusters. The saturation magnetic moment of the amorphous alloys takes a broad maximum around x = 0.10, which is analogous with that of the crystalline alloys. The Curie temperature rapidly decreases with increasing Mn concentrations. The magnetic moment and the Curie temperature of the amorphous alloys are higher than those of the crystalline counterparts. Magnetic frustrations between ferromagnetic and antiferromagnetic interactions bring about a spin-glass state above x = 0.35.

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Magnetic properties of La(Fe_0.875Al_0.125)₁₃ intermetallic compound have been investigated. The present compound shows a metamagnetic transition from an antiferromagnetic to ferromagnetic state by applying external magnetic field. The temperature dependence of the metamagnetic transition field indicates a broad maximum at 160 K. With increasing temperature, triple transitions from the antiferromagnetic to ferromagnetic, to antiferromagnetic and finally to paramagnetic state occur in 25 kOe due to the characteristic temperature dependence of the transition field. The magnetic entropy change due to the metamagnetic transition has been estimated by using the Clausius-Clapeyron relation and increases linearly with temperature in low temperatures. This behavior implies that the 3d band structure is changed by the metamagnetic transition.

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Temperature dependence of magnetic susceptibility and electrical resistivity of (Ce_1-xLa_x)Pb₂ compounds have been investigated in order to study the effect of substituting La for Ce in a heavy fermion system. The effective magnetic moment estimated from the Curie-Weiss law agrees with that of the theoretical trivalent Ce-ion and independent of the La concentration in high temperatures. The temperature dependence of the magnetic contribution to the electrical resistivity continuously changes from a dense to dilute Kondo regime with increasing La concentration. This behavior would be correlated to a reduction of the Kondo temperature by the substitution of La for Ce.

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Magnetic and specific heat measurements of Ce₅Pb₃ compound with a Mn₅Si₃-type structure have been carried out. The magnetic susceptibility shows two peaks at 3.5 and 20.5 K due to the magnetic transitions. The paramagnetic Curie tempertature and the effective magnetic moment obtained from the magnetic susceptibility are -8.2 K and 2.6μ_B, respectively. These results indicate that 4 f electrons are localized in high temperatures and the ground state is antiferromagnetic. The electronic specific heat coefficient, γ, is about 120 mJ/Ce-mol K², and the Debye temperature, θ_D, is estimated to be 150 K. From these results, it is concluded that Ce₅Pb₃ is an antiferromagnetic heavy-fermion compound. The Néel temperature T_N of Ce₅Pb₃ compound is higher than that of other Ce-Pb compounds, which is related to the two kinds of Ce sites.

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A new system of RCo_12-xAl_x (R=Y, Sm and Gd) compounds with TbCu₇-type structure has been successfully synthesised. Both thermomagnetic analysis and x-ray diffraction measurements show that all the compounds are almost of single phase and crystallize in the TbCu₇-type structure. The Curie temperature T_C is 921 K for YCo_10.5Al_1.5, 909 K for SmCo_10.5Al_1.5, 952 K for GdCo_10.5Al_1.5 and 1046K for GdCo₁₁Al. X-ray diffraction patterns of magnetically aligned powder samples indicate that all compounds investigated exhibit uniaxial anisotropy at room temperature. The anisotropy fields and saturation magnetizations of these compounds have been obtained by means of singular point detection (SPD) technique and magnetic isotherm measurement, respectively.

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Magentostriction measurements in highly-oriented ribbons of (Er_1-xTb_x)₂Fe₁₄B with 0≤x≤0.45, fabricated by a rapid-quenching method have been performed in order to investigate the lattice deformation at the spin reorientation (SR) transitions. The c-axis of the tetragonal cell was found to be aligned perpendicular to the ribbon surface. The sum of the longitudinal and transverse magnetostriction λ_//+λ_⊥, with fields applied within the ribbon plane, took a maximum at successive SR temperatures. A model calculation of the volume change ΔV/V was made by assuming that only the crystalline electric field (CEF) potentials at Er and Tb sites affect the volume change. This calculation showed that ΔV/V exhibits a sharp peak at SR temperatures, which is in accordance with the experimental peaks of λ_//+λ_⊥.

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The substitutional effect of Y or Pr for Nd on spin reorientation and magnetocrystalline anisotropy of (Nd_1-xRE_x)₂Fe₁₄B (0≤ x ≤0.75) has been investigated from magnetization curves of magnetically aligned powders. The experiments have shown that Y- or Pr-substitution for Nd decreases both the spin reorientation temperature (T_SR) and spin reorientation angle. The decrement of T_SR by Y-substitution was within 15 K. The Pr-substitution, however, considerably decreased T_SR with the ratio of ΔT_SR = -1.35 K/Pr at. %. The decrement of spin reorientation angle in the composition range of 0 ≤ x ≤ 0.5 is about ΔSRA =-0.073°/Y at. % and ΔSRA =-0.258°/Pr at. %, respectively. The experiments on magnetocrystalline anisotropy expect the disappearance of spin reorientation at about x>0.9 for RE=Y and at about x>0.8 for RE=Pr at 4.2 K.

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The results of DC magnetization, AC susceptibility, specific heat and magnetic relaxation measurements on a well-annealed polycrystalline U₂NiSi₃ sample are reported. The temperature dependencies of the DC magnetization and AC susceptibility show a cusp at a characteristic temperature T_f and a weak ferromagnetic transition at T_C>T_f. The temperature T_f strongly depends on the applied magnetic field and frequency. Below T_f the magnetic relaxation measurements reveal a decay of the isothermal remanent magnetization versus time which is drastically slower than above T_f. No anomalies around T_f are observed in the specific heat data which rules out the existence of usual long-range spatial magnetic order at T_f. These results can be considered as clear evidence for the formation of a re-entrant spin glass state in U₂NiSi₃. The necessary randomness in the U-U magnetic exchange interactions arises from a statistical distribution of Ni and Si atoms on the crystallographic sites of the U₂NiSi₃ crystal lattice.

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We present a soft x-ray magnetic circular dichroism (SXMCD) study of the electronic and magnetic states of ferromagnetic CoS₂ and ferrimagnetic Fe₇S₈ and Fe₇Se₈. An application of the SXMCD spin and orbital sum rules to the Co L_{2, 3} and Fe L_{2, 3} SXMCD spectra gives reliable individual spin and orbital magnetic moments. We argue the electronic structure of these compounds and propose new pictures for the spin-polarized density of states on the basis of the experimentally determined magnetic moments.

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The Fe doped Cd_0.62Mn_0.38Te has some magnetic characteristics similar to spin-glasses even at room temperature, e. g., the thermal irreversibility of magnetic susceptibility, the time-dependent remanent magnetization and so on. We analyzed the decay curve of thermoremanent magnetization (TRM) observed at temperatures from 100K to 260K in comparison with that in the low temperature spin-glass region. Both the decay curves were well fitted by a stretched exponential. The relaxation time τ evaluated from the high temperature data is longer compared with the low temperature curve, while the time-stretched exponent n is small. We discuss the high temperature spin-glass-like relaxation of TRM based on the ferromagnetic cluster formation caused by the exchange interaction between carriers and magnetic ions, i.e., bound magnetic polaron.

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We investigated the saturation magnetization and structure of iron foils treated by nitrogen plasma irradiation. The surface of each nitrided foil was removed step by step by electropolishing, and the saturation magnetization of the nitrided foil was then measured. X-ray diffraction patterns were taken from the electropolished surface at each step. Various iron nitrides were formed at all depths of foils nitrided for 5 hours or more, and their quantity increased with the nitriding time. The outermost region of the surface layer irradiated with nitrogen plasma was composed of γ′-Fe₄N and ε-Fe₃N, and the inner region was composed of α′-martensite. The saturation magnetization of α′-martensite in a foil nitrided for 13 hours was 223 emu/g. The nitrogen concentration of α′-martensite in the foil irradiated with nitrogen plasma was 0.5 atomic percent.

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The magnetic properties of trivalent vanadium oxide system, LuVO₃, were investigated by the measurements of DC magnetization and AC magnetic susceptibility. The antiferromagnetic Weiss temperature of -106K and effective moment of 2.68μ_B were obtained from the Curie-Weiss fitting. The three steps of magnetic transitions were observed in DC magnetic susceptibility at about 107K, 86K and 72K. These magnetic behaviors should be discussed by the complex exchange interactions in this system.

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The linear and non-linear ac-susceptibilities of the Mott insulator YVO₃ were measured using a Hartshorn mutual inductance bridge. It is found by the temperature dependence of ac-susceptibilities that there are two magnetic phase transitions at 72.1 and 112.0 K. Above 112K, the values of linear and non-linear susceptibilities qualitatively consist with the result of the mean-field theory. It is verified that there is a power-law dependence between linear and non-linear susceptibilities, which is predicted by the mean-field theory.

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The magnetic properties of an itinerant ferromagnet SrRuO₃ have been determined in the hydrostatic pressure, temperature and magnetic field range 0-13.2 kbar, 4.2-300 K, and 0-90 kOe, respectively. The pressure derivatives of the Curie temperature and saturation magnetization at 4.2 K are found to be -0.67 K/kbar and -0.47 emu/g kbar, respectively

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We have measured the resistivity and the ultrasonic sound velocity of La_0.7Ca_0.3MnO₃ as functions of temperature and magnetic field. As the temperature is lowered through T_c, where the magnetic phase transition occurs, the sound velocity increases rapidly in the narrow temperature region around T_c. The region where the velocity change occurs shifts up to higher temperatures, as a larger magnetic field is applied. The qualitative behavior of the sound velocity as a function of temperature may be explained in terms of phonon hardening which is due to the combined effect of the double-exchange and the strong electron-phonon interaction.

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We have measured the magnetization, susceptibility, specific resistance, X-ray and neutron diffraction data of the series Ho_xCa_l-xMnO₃ (x≤0.5; step width Δx = 0.1 or less). The compounds analyzed have distorted perovskite structures: they are orthorhombic for 0≤x≤0.13, and have an orthorhombic to monoclinic phase transition for 0.13≤x≤0.33. Ho ions are paramagnetic for 4 K≤T≤300 K. Their magnetization and susceptibility at low temperatures are, however, reduced from what one expects for free ions. We calculate a crystal field correction M_Ho(T, H) and χ_Ho(T). The resulting data for Mn show a reduced magnetic moment (x≥0.2) and a ferromagnetic phase at x = 0.1 ± 0.05 with ordering temperatures T_N/T_C ≈ 110 K. These results show that (Ho_xCa_1-x)MnO₃ belongs to the family of the giant magnetoresistance compounds (La_xCa_1-x)MnO₃ with, however, the ferromagnetic phase occuring at x = 0.1 as compared to x = 0.67 in the La-compound.

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