S. Yuasa

Transparent magnetic fluid: preparation of YIG ultrafine particles

Abstract In order to prepare transparent magnetic fluid, yttrium iron garnet ultrafine particles ranging in size from 10 through 30 nm are synthesized by hydrolysis of metal alkoxides. Differential thermal analysis, X-ray diffraction analysis, electron micrography and magnetization measurements are carried out on these particles to investigate the calcination condition and particle sizes.

Giant room temperature volume magnetostriction in an FeRhPd alloy

Abstract Thermal expansion and magnetization in the temperature range 150–800 K and magnetostriction measurements using a high pulsed magnetic field up to 15 T have been performed on the alloy Fe 1.005 Rh 0.85 Pd 0.15 ) 0.995 . We have found a huge volume magnetostriction at room temperature ( ω = 8×10 −3 ), which appears at a determined critical value of the applied magnetic field. These results were explained on the basis of recent band structure calculations.

Magnetic properties and phase transition in bct FeRh1−xPtx alloys

Magnetic properties of the pseudobinary bct FeRh1−xPtx alloys were investigated from the viewpoints of a lattice distortion and a magneto-volume effect. The axial ratio, ca, varies from 1.185 to 1.359 with increasing x from 0 to 1.0. In x < 0.72, the Curie temperature was found to be lower than the antiferromagnetic-ferromagnetic transition temperature and, consequently, the first order phase transition from the antiferromagnetic state to the paramagnetic state was observed.

Magnetostriction and thermal expansion measurements on FeRh1−xPtx alloys

We report high‐field magnetostriction and thermal expansion measurements in FeRh1−xPtx (x=0.75, 0.765, and 0.7) compounds. From the thermal expansion measurements we have observed the para‐ferromagnetic and ferro‐antiferromagnetic transitions for x=0.75 and 0.765, and the para‐antiferromagnetic transition in the 0.7 compound. The volume expansion associated with the first‐order transitions has been determined. The results of the magnetostriction measurements are complex and are explained here on the basis of an induced transition from an antiferromagnetic to a ferromagnetic state, induced by the applied magnetic field.

Structural phase transition and magnetic properties of FeRh1−xCox alloys

Abstract FeRh 1− x Co x ( x = 0.0, 0.02, 0.04) alloys pulverized by filing have fcc structure. The fcc FeRh alloy was paramagnetic and stable at room temperature, and it transformed to a ferromagnetic bcc structure above about 500 K. The magnetic field applied to the alloy decreases the transformation temperature.

Magnetic properties of bcc FeRh{sub 1{minus}x}M{sub x} systems

The magnetic properties of ordered bcc FeRh 1-x M x alloys (M=Fe, Co, Ni, Pd, Ir and Pt) were studied, in terms of correlations among the antiferromagnetic-ferromagnetic transition temperature T 0 , Curie temperature, magnetization, and lattice constant. Substitution of the 3d element M for Rh diminishes the transition temperature T 0 , since the large magnetic moment of the M atom stabilizes the ferromagnetism. Moreover, a first-order antiferromagnetic-paramagnetic transition was observed in an FeRh 1-x Ir x system. The mechanism of such first-order phase transitions can be explained phenomenologically by introducing magneto-volume coupling into a model based on the SCR theory. The ground state properties of FeRh and FeRh 1-x Pd x are well explained by first-principle band calculations based on the linearized muffin-tin orbital method.

Magnetic Properties of bcc FeRh 1-x M x Systems

The magnetic properties of ordered bcc FeRh 1-x M x alloys (M=Fe, Co, Ni, Pd, Ir and Pt) were studied, in terms of correlations among the antiferromagnetic-ferromagnetic transition temperature T 0 , Curie temperature, magnetization, and lattice constant. Substitution of the 3d element M for Rh diminishes the transition temperature T 0 , since the large magnetic moment of the M atom stabilizes the ferromagnetism. Moreover, a first-order antiferromagnetic-paramagnetic transition was observed in an FeRh 1-x Ir x system. The mechanism of such first-order phase transitions can be explained phenomenologically by introducing magneto-volume coupling into a model based on the SCR theory. The ground state properties of FeRh and FeRh 1-x Pd x are well explained by first-principle band calculations based on the linearized muffin-tin orbital method.

Magnetism of FeRh1−xPdx system — band calculation

Abstract The first-principle spin-polarized energy band calculations were performed using the LMTO method in order to determine the total energy and the local moments of the body-centered tetragonal FeRh 1− x Pd x alloys as a function of the axial ratio c a from 0.8 to 1.358. The calculations show that there are competing ferromagnetic and antiferromagnetic states in FeRh alloy with c a =1 and in FeRh 0.5 Pd 0.5 alloy with c a =1.238 . The first-order magnetic transitions can therefore be induced at finite temperatures as have been observed experimentally in both alloys.

Time evolution of magnetization in the FeRh system near antiferromagnetic‐ferromagnetic transition temperature (abstract)

The body‐centered cubic FeRh is known to exhibit a first‐order phase transition from antiferromagnetic to ferromagnetic at about 400 K, accompanied by a volume expansion of about 1%. The time evolution of the magnetization M of ordered Fe0.5Rh0.5 and FeRh0.958Pt0.042 just below and above the transition temperature (T0) was measured as functions of temperature and magnetic field. Around T0, the magnetization increased logarithmically with time up to M*(=41 emu/g), the value of which indicates that the ferromagnetic grains occupy one third of the antiferromagnetic matrix. When M=M*, there appeared a jump in M. After that, M varies as M(t) =M∞[1−exp(−t/τ)], where τ is a relaxation time. It should be noted that the value of M* is independent of both temperatures and external magnetic fields. Microscopic observation and x‐ray diffraction measurement showed that the ferromagnetic grains nucleated in the antiferromagnetic matrix began to grow with time just below T0. In this work, the time evolution of the phase...