S. Anzai

Crystal structure of magnesium ditelluride

The crystal structure of MgTe2 has been investigated by X-ray diffraction method. The intermetallic compound crystallizes in the pyrite-type structure (Th6-Pa3) with the parameters u = 0·389, Debye temperature ΘD = 210°K and lattice constant a = 7·025±0·002 A. This is the first compound found in the nontransition-metal chalcogenide with pyrite-type structure.

Pressure effect on the Curie temperatures of Cr1-δTe compounds

The pressure derivatives of the Curie temperatures for δ = 0.27, 5 = 0.29 and δ = 0.35 are -5.4 ∓ 0.2, −3.4 ∓ 0.2 and −1.6 ∓ 0.1 in units of K/kbar, respectively. The pressure derivative of the transition temperature between the canted ferromagnetic and the ferromagnetic states is + (8.5 ∓ 0.5) K/kbar for δ = 0.27.

Impurity effects of the 3d transition metal atoms on the first‐order magnetic and electrical transition in NiS

In the NiAs‐type Ni1−xMxS (M: the 3d transition metal impurities), the solubility limits xL are determined to be 0.077±0.005 for M:Ti, 0.04±0.01 for M:Cr, 0.001±0.002 for M:Mn, 0.060±0.005 for M:Co, and 0.015±0.005 for M:Cu. The first‐order transition temperature Tt (between the antiferromagnetic less‐conductive and the Pauli‐paramagnetic high‐conductive states) is investigated as a function of x for M:Ti, Cr, Co, and Cu (as described on M:V in our previous paper). The lattice parameters c and a are also investigated. The larger x gives the lower Tt for these M, except in the lower x for M:V or Cr. The following features are found on M:Ti (similar to V and Cr): a Curie–Weiss‐type susceptibility is superimposed on the constant Pauli‐paramagnetic one in temperatures above Tt; the sign of dθ(T<Tt)/dT (θ: thermoelectric motive force) changes from plus to minus at a critical concentration. The ratio c/a hardly depends on x in the cases of more than half filled M (Co and Cu), while it increases in x in the less...

Localized versus itinerant character of d electrons in NiS: Photoemission spectroscopic study

Abstract The electronic structure of NiS on both sides of the metal-nonmetal transition has been studied by photoemission spectroscopy using synchrotron radiation and compared with band structure calculations. Interplay between Ni d-ligand hybridization, electron correlation, exchange interaction, and d-band formation is discussed.

Nonvolume effect of Rh substitution on the metal‐nonmetal transition in NiS

The lattice parameters a (x) and c (x), the transition temperature Tt(x), and the heat of transition ΔHt(x) are investigated in the NiAs‐type Ni1−xRhxS (the solubility limit is x=0.076). a (x) and c (x) increase with increasing x, while Tt(x) decreases and finally disappears at x=0.072. This behavior is contrasted with those observed on the 3d‐transition‐metal substitutions and the pressure experiments. Such a difference is understood with the change in the electronic state, at a constant volume (nonvolume effect), due to the 4d‐transition‐metal impurity substitution. Contributions of the nonvolume effect on this transition are estimated from Tt(x) and ΔHt(x) through the Lidiard model improved by Anzai and Ozawa. They are discussed on the basis of the difference in the electron configurations between the 4d‐ and 3d‐transition‐metal elements.

Metal‐nonmetal transition in NiS under pressure

The thermodynamical model of Lidiard for an itinerant antiferromagnet is extended to involve the strain energy and the volume dependence of the energy gap between up‐ and down‐spin bands. The model is manipulated to fit the pressure effect of metal‐nonmetal transition temperature and its first‐order characteristics in NiS. Here, the volume compressibility used is measured to be 1.1×10−3 kbar−1. Changes in magnetic moment on the Ni sublattice and in enthalpy at the transition temperature are calculated from the obtained parameters and compared with the available experimental data. The nature of metal‐nonmetal transition in NiS under pressure is discussed. Present study constitutes the first attempt to understand the energetics of the metal‐nonmetal transition in NiS throughout its T‐P diagram.

Vanadium‐substitution effect on the first‐order magnetic and electrical transition in NiS

The cell volume ν of the NiAs‐type Ni1−xVxS increases with increasing x below the solubility limit xL = 0.076±0.003. The following results of the V substitution are discussed on the basis of the strongly perturbed dilute‐alloy model which is modified to the splitting eg ‐band diagram for NiS. (1) The transition temperature Tt and the heat‐of‐transition decrease with increasing x in the high x region below xL. This behavior is in contrast with the volume effect (∂Tt/∂ν ≳ 0) deduced from the previous pressure experiment. (2) The susceptibility at 300 K ( ≳ Tt) is enhanced with increasing x. (3) Below Tt, dominant carriers are holes in the sample with x = 0.02, while they are electrons in x = 0.05.

Magnetic susceptibility, electrical resistivity and thermal expansion coefficient of NiAs-type V1−xCrxSe

Abstract V 1− x Cr x Se(0.05⩽x⩽0.83) shows a temperature dependence of the magnetic susceptibility χ which is similar to that of CrSe. At small x , the magnetic transition temperature T t ( x ) and the Weiss constant θ p ( x ) decrease with decreasing x , while the effective number of Bohr magnetons per Cr ( P eff ) significantly increases.

Long‐Time Decay of Thermoremanent Magnetization through Stepwise Changes of the Reentrant Spin‐Glass‐Like State in the Ni2In‐Type Mn7Sn4

The zero-field-cooled magnetization at the magnetic field H = 300 Oe shows anomolous kinks at T A and T e (> T A ) far below the reentrant spin-glass-like transition temperature T f (above which a long-range ferrimagnetic ordering is set up). The irreversibility between the zero-field-cooled and the field-cooled magnetizations, and the time decay of the thermoremanent magnetization (σTRM) are observed below the ferrimagnetic Curie temperature T C . The decay feature can be described by Ogielskis power law σTRM = At -a whose a exhibits peaks at T A , T B , T f and T C . The peak of α at Te can be fitted by the combination of Ising type and Ginzburg-Landau type expressions. Three stepwise changes of the spin-glass-like state below T f and the feature of the coexistence of short-range spin-glass and long-range magnetic ordering components above T f are discussed.

Photoemission Study of the Electronic Structure of the Ferromagnetic Cr1-δTe System

The electronic structure of Cr1-δTe (δ=0.05, 0.25, 0.375) has been studied by photoemission spectroscopy. Structures near the Fermi level are qualitatively explained by the density of states (DOS) given by band-structure calculations, but significant discrepancies exist in the higher binding energy region. Configuration-interaction cluster-model calculations have been performed and the overall experimental features have been explained, indicating significant electron correlation effects in these compounds.