Masuhiro Yamaguchi

Successive phase transitions in ferromagnetic YCo3

Abstract The magnetization process of YCo 3 was measured at low temperatures in pulsed ultrahigh magnetic fields up to 110 T. The result indicates that successive metamagnetic transitions without hysteresis occur at 60 and 82 T. The magnetization changes from 0.72 to 0.88μ B /Co and from 0.88 to 1.23μ B /Co by both transitions. Above 90 T, the magnetization is completely saturated.

Influence of hydrogen on the magnetic properties of YCo compounds

Abstract The effect of hydrogen absorption on the magnetic properties of the Y2Co7Hx and the YCo3Hx systems was examined in situ. The two systems show similar β and γ phase formation and magnetic behaviour. The β phase exhibits the anomaly that a slight hydrogen enrichment induces a substantial increase in the cobalt moment which varies from a minimum on the low concentration side (0.13 μB in Y2Co7H2 and 0.15 μB in YCo3H) to a maximum on the high concentration side (1.2 μB in Y2Co7H3 and 0.7 μB in YCo3H2). These maximum values are almost equal to those in the respective uncharged compounds. The cobalt moment in the γ phase decreases with increasing hydrogen concentration in the same way as in ordinary cobalt-based ferromagnets. Both systems tend to lose ferromagnetism in the most hydrogenated compounds Y2Co7H8 and YCo3H4. The anomalous dependence of the cobalt moment on composition is discussed.

Magnetic Properties of Cr3Te4 in Ferromagnetic Region

Single crystals of Cr 3 Te 4 with the pseudo-NiAs type structure have been made by chemical transport method in order to investigate the anomaly below 80 K. The saturation moment at 4.2 K is equal to 1.79±0.03 µ B per Cr 1- x Te (x=0.25), and the Curie temperature is 316 K. The magnetization only in the direction to the a -axis shows the anomaly that the saturation field increases abruptly below 80 K, which corresponds to the Neel point proposed by Andresen. But on the contrary to his result, the easy axis of the moment is parallel to the c -axis in the whole ferromagnetic region and antiferromagnetic order appears only in the c -plane. By a spin echo method, two nuclear magnetic resonance absorption lines of Cr 53 -nuclei are observed at 45.3 and 57.5 MHz at 4.2 K. The resonance frequencies increase remarkably below 80 K. This fact may support subsidiarily the existence of the antiferromagnetic order below 80 K.

Magnetic studies of hydride phase transformations in NdCo5Hx, PrCo5Hx and LaCo5Hx☆

Abstract Hydride-phase transformations in the ferromagnetic RCo 5 H x systems (R  Nd, Pr and La) are studied from the magnetic behaviour of the systems under the influence of hydrogen. In magnetization-temperature isobars stepwise changes in magnetization indicate the transformations between the α, β II , β I and γ phases in NdCo 5 H x and PrCo 5 H x and between the α, β I and γ phases in LaCo 5 H x . The limiting composition of the γ phase at 238 K is x = 4.7 ± 0.1 for NdCo 5 H x and x = 4.8 ± 0.1 for PrCo 5 H x . The change in enthalpy for each transformation is determined from the magnetic behaviour.

Thermal expansion and high field magnetization of a single crystal γ-phase hydride YCo3H3.9

Abstract Lattice parameters and magnetization have been measured for a single crystal hydride YCo 3 H 3.9 . This hydride has an orthorhombic distortion and exhibits unusual changes in the lattice parameters. The hydride becomes antiferromagnetic and a metamagnetic transition occurs along the c -axis. The magnetization above the transition is slightly lower than that of YCo 3 along the c -axis.

Field induced magnetic phase transition and magnetostriction in ErCo3, HoCo3 and Nd2Co7 single crystals

Abstract Magnetization and magnetostriction measurements have been carried out for single crystals of ErCo 3 , HoCo 3 and Nd 2 Co 7 in magnetic fields up to 7 T at various temperatures. Field-induced phase transitions from collinear to noncollinear magnetic structure are observed in these compounds. The temperature dependence of the transition field can be explained by considering the temperature variation of the magnetic anisotropy for different magnetic sublattices. The field-induced transition is accompanied by the large linear and volume magnetostriction.

Shift in the chemical equilibrium of the LaCo5H system by strong magnetic fields

Abstract The equilibrium hydrogen pressure in the β+γ region of the LaCo5-H system has been observed under the influence of magnetic fields up to 14 T. The logarithmic pressure change, In(PH/P0), is 0.19 in 14 T. This corresponds to a 21% change in the equilibrium constant.

High field magnetization of Y2Co7 and YCo3 hydrides

Abstract The magnetization curves for the Y2Co7Hx and the YCo3Hx systems have been measured at 4.2 K in the pulsed high magnetic fields up to 280 kOe. The metamagnetic transition is observed in the β and the γ hydrides except for Y2Co7H3 and YCo3H1, which is interpreted in terms of the itinerant electron metamagnetism.

Itinerant-electron metamagnetism of

Electronic structures of the pseudo-binary compound with the -type hexagonal structure are calculated in the self-consistent linear muffin-tin orbital method within the atomic sphere approximation, by taking into account the preferential occupation sites for Ni. The calculated bulk moment disappears abruptly near 60% Ni concentration. Above the critical concentration of Ni, a metamagnetic transition from the paramagnetic to the ferromagnetic state is found to occur. These calculated results are consistent with the recently observed ones. It has been shown that the anomalous magnetic behaviours of can be explained by the detailed shape of the local density-of-states curve of the 3d-transition-metal atoms at the 3g site near the Fermi level.

Crystal structure of γ-phase RCo3H∼4 hydrides

Abstract γ-phase RCo3D∼4 deuterides with R ≡ Y and Er were studied by neutron diffraction analysis at room temperature in the paramagnetic state. Deuterium atoms are distributed over three types of interstitial site 18h2, 36i1 and 36i2 with occupancies of about 90%, 35% and 10% respectively. The deuterium site occupation is compared with that for β-phase RCo3 hydrides and with RCo2 and RCo5 structures from which the RCo3 lattice can be constructed.