S Yashiro

Magnetic properties of RFe1−xMnxO3 (R=Pr, Gd, Dy)

A novel magnetic transition was observed in a perovskite-type oxide of PrFe1−xMnxO3 (R=Pr, Gd, Dy; 0<x<0.6). When iron ions in weak-ferromagnetic RFeO3 are replaced by manganese ions, the Curie temperature TC decreases monotonically as the Mn content increases, and a spin-reorientation transition from antiferromagnetism to weak-ferromagnetism appears at low temperature. The transition temperature TR depends on the Mn content and increases with increasing x, coinciding with the TC at a Mn content near x=0.5. The spin-reorientation transition seems to be caused by a change in the superexchange interaction and magnetocrystalline anisotropy introduced by the substitution of Mn. The effect of Mn-substitution on the electric resistivity was also studied and compared with that of Ca-substitution in the Pr1−xCaxFeO3 system. Ca-substitution has a remarkable effect on the resistivity but Mn-substitution causes a slight change in it.

Magnetism and transport properties of Hf1−xTaxFe2 and Mn2−xCrxSb

Abstract The magnetism and transport properties of Hf 1− x Ta x Fe 2 (0.1≤ x ≤0.2) and Mn 2− x Cr x Sb ( x =0.1) were studied. Hf 1− x Ta x Fe 2 ( x >0.15) has a successive magnetic transition from ferromagnetism to paramagnetism via antiferromagnetism at temperatures between 150 and 350 K, and the transition has a considerable effect on the transport property. In particular, a specimen with x =0.155 shows a metamagnetic transition near room temperature, and a significant magnetoresistance as large as 12% is observed in accordance with the metamagnetic transition. Mn 1.9 Cr 0.1 Sb, which has a first-order magnetic transition from antiferromagnetism to ferrimagnetism at about 300 K, also shows a field-induced magnetic transition at 300 K, and the transition strongly affects the transport property. A giant magnetoresistance as large as 30% was observed at about 300 K under an applied field of 20 kOe. The metamagnetic transition seems to give rise to giant magnetoresistance via s–d scattering.

New intermetallic compounds found in Hf–Ni–Ge and Hf–Pt–Ge systems

Abstract New intermetallic compounds, Hf3Ni4Ge4 and HfPtGe, were found and their crystallographic, electric and magnetic properties were characterized. Hf3Ni4Ge4 has an orthorhombic structure (space group Immm) with lattice constants of a=1.2873 nm, b=0.6484 nm, and c=0.3892 nm and shows typical Curie-paramagnetic behavior between 2 K and 300 K and a metallic temperature dependence of the resistivity at temperatures between 10 and 250 K. HfPtGe has an orthorhombic structure (space group Pnma) with lattice constants of a=0.6603 nm, b=0.3950 nm, and c=0.7617 nm and shows diamagnetism and a metallic temperature dependence of the resistivity.

Magnetism and transport properties of Nd6Fe13−xAl1+x crystals

Abstract Nd 6 Fe 13− x Al 1+ x ( x =2.2 and 3.5) crystals were grown by the self-flux method, and their crystallographic, magnetic and electric properties were investigated. Nd 6 Fe 13− x Al 1+ x , which crystallizes in a tetragonal structure of space-group I4/mcm, shows peculiar successive magnetic transitions. In particular, Nd 6 Fe 9.5 Al 4.5 shows transitions at 20 K, 56 K and 128 K, and the spontaneous magnetization M s at 5 K (87.5 emu/g) can be explained by assuming ferromagnetic Fe sublattices (4d↑16k↑16l 1 ↑16l 2 ↑) and ferrimagnetic Nd sublattices (8f↓16l↑). Nd 6 Fe 9.5 Al 4.5 seems to adopt ferrimagnetism in which the spontaneous magnetization is parallel to the 〈100〉 directions at temperatures below 20 K. A small ferromagnetic moment component, which is induced by canting of the antiferromagnetically coupled spins along the [001] direction, exists in the [100] direction at temperatures of 20 K T T T

Magnetism and transport properties of HfMSi (M=Pt, Pd) and HfRh1−xPdxSi

Abstract The crystallographic, electric, and magnetic properties of the new intermetallic compounds HfMSi (M=Pt or Pd) and the superconductivity of HfRh 1− x Pd x Si were studied. The crystal structure of HfPtSi and HfPdSi could be refined assuming an orthorhombic structure (space group Pnma ) and lattice constants of a =0.6549 nm, b =0.3883 nm, and c =0.7506 nm for HfPtSi and a =0.6570 nm, b =0.3874 nm, and c =0.7565 nm for HfPdSi. Both compounds are metallic and show diamagnetic behavior below 300 K. A small effective electron mass is thought to be a reason for the diamagnetism of HfMSi (M=Pt or Pd). In the HfRh 1− x Pd x Si system, the superconductivity of HfRhSi ( T c =2.2 K) is suppressed by replacing Rh by Pd. The Pd content dependence of the Pauli paramagnetic susceptibility suggests that reduction of the density of states at the Fermi level is a possible cause of the suppression of superconductivity in the HfRh 1− x Pd x Si system.

Crystal growth of rare earth–iron intermetallic compounds by the flux-creep-up method

A new flux method for the crystal growth of rare earth-iron intermetallic compounds was developed. In this method, the rare-earth flux creeps up the inner surface of a BN-coated crucible during the cooling process, and free-standing crystals are left on the bottom of the crucible. This method was applied to the crystal growth of compounds in Sm-Fe and Nd-Fe systems, and crystals of SmFe 2 , SmFe 3 , Sm 6 Fe 23 , and Nd 6 Fe 13-x Al 1-x were grown for the first time. In particular, SmFe 7 is a new phase in the Sm-Fe system with high performance as a permanent magnet. Since the chemical composition of the mixture in the crucible changes in accordance with the creep-up of the flux, this method may be promising in the search for new phases as well as for the crystal growth of known materials.

Magnetic properties of Sm6Fe23 crystal

A single crystal of Sm6Fe23 was prepared by means of a modified self-flux method, and its crystallographic magnetic properties were studied. Sm6Fe23 has the cubic Th6Mn23-type structure (space group Fm3m) with a lattice constant of a=1.2187±0.0006 nm. The easy axis of magnetization is parallel to the 〈111〉 direction. Its magnetic moment per unit formula deduced from the saturation magnetization is 59 μB at 5 K, a value that is consistent with the value calculated assuming ferromagnetic coupling between the Sm and Fe sublattices. The cubic anisotropy constants K1 and K2 estimated from the magnetization curves of the [111], [110], and [100] directions are −2.7×106 and 6.3×105 erg/cm3, respectively. The anisotropy field HA calculated from the anisotropy constants is 6.1 kOe.

New equiatomic silicides of MM′Si (M=Nb, Ta;M′=Pt, Rh) and superconductivity of Ta1−xNbxPtSi

Abstract The present study focuses on the crystallographic, electric, and magnetic properties of the new intermetallic compounds of NbPtSi and MRhSi (M=Nb, Ta) and the substitution effect on the superconductivity of TaPtSi in the system of Ta 1− x Nb x PtSi (0≤ x ≤1). The crystal structure of NbPtSi and MRhSi was refined assuming an orthorhombic Co 2 Si structure of the space group Pnma . MRhSi (M=Nb, Ta) has metallic conductivity and shows diamagnetic behavior at temperatures between 1.7 and 350 K. On the other hand, NbPtSi shows paramagnetic behavior with metallic conduction. In the Ta 1− x Nb x PtSi system, the superconductivity of TaPtSi ( T c =3.5 K) is suppressed by Nb substitution. The Nb-content dependence of the Pauli-paramagnetic susceptibility suggests that reduction of the density of states at the Fermi-level is a possible reason for the suppression of superconductivity.

Magnetic properties of Sm(Fe1−xAlx)7 crystals

Abstract Sm(Fe 1− x Al x ) 7 ( x =0, 0.047, 0.07 and 0.12) crystals were grown by the self-flux method, and their crystallographic and magnetic properties were investigated. Sm(Fe 1− x Al x ) 7 crystallizes in a tetragonal structure of the space group P4 2 /mnm , and aluminum occupies the iron site. The structure is very similar to that of Nd 2 Fe 14 B except that the boron sites are vacant. The Curie temperature, T C , increases with a modest Al substitution in spite of little changes in the saturation magnetization M s . However, both T C and M s decrease for a higher Al substitution. All the specimens have negative K 1 and positive K 2 . The easy axis of magnetization is parallel to the [100] direction since K 1 +2 K 2 K 1 +2 K 2 decreases and becomes closer to zero with increasing Al content, aluminum substitution seems to be ineffective to change the easy direction from the basal plane to the c -axis.

Magnetic properties of the Laves-phase compounds Fe1-xCoxBe2

Abstract The magnetic properties of polycrystalline and single-crystalline Fe 1− x Co x Be 2 were investigated by magnetization, Mossbauer, and torque measurements. Curie temperature (880 K at x =0) and magnetic moment (1.94 μ B at 5 K for a specimen with x =0) decrease with increasing content of Co. The Co-content dependence of the magnetic moment could be explained by considering magnetic moments of Co. Co seems to have a magnetic moment induced by an interaction between Co and the nearest neighbor iron atoms. Hexagonal anisotropy constants were determined as K u1 =9.7×10 5 erg/cm 3 and K u2 =9.9×10 4 erg/cm 3 for a specimen with x =0 and K u1 =3.4×10 5 erg/cm 3 and K u2 =3.3×10 4 erg/cm 3 for x =0.1. Co substitution is ineffective to the improvement of the magnetic anisotropy of FeBe 2 .