Katsuhiko Koui

Itenerant metamagnetism of the Co-sublattice in the Y1−xNdxCo3 system in ultrahigh magnetic fields up to 110 T

Magnetization measurements have been carried out for Y1−xNdxCo3 compounds with 0⩽x⩽1 in ultrahigh magnetic fields up to 110T. The compound exhibits two metamagnetic transitions of the Co sublattice to a higher moment state. Both transition fields decrease with increasing Nd concentration due to the exchange field from the Nd sublattice acting on the Co sublattice. From the concentration dependence of the transition fields the average exchange parameter between Nd and Co is estimated to be JNdCo = 2.0 × 10-22 J. The spontaneous Co moment and the Curie temperature also exhibit an anomalous increase with Nd concentration, which originates from the transitions.

Co metamagnetism in Y1−xNdxCo3 under ultra-high magnetic field

Abstract The magnetization of Y 1−x Nd x Co 3 (0 ≤ x ≤ 1) was measured up to 110 T. YCo 3 exhibits two successive transitions to a higher moment state of Co. When a part of Y is replaced with Nd, two transition fields decrease owing to the positive exchange interaction between Nd and Co. From these results, the exchange interaction parameter between Nd and Co has been evaluated to be 2.13x10 −22 J. The volume magnetostriction was measured in high magnetic field up to 40 T with a capacitance method. A large volume change has been observed with the growth of the Co moment.

The Haldane State in CsNiCl 3 Detected by Magnetization Measurements –Observation of Quantum-Classical Crossover and the Valence Bond Solid State–

We have confirmed from susceptibility and magnetization measurements that the Haldane state really exists in 1D phase of CsNiCl 3 which undergoes 3D ordering at T N =4.8 K. The observed susceptibility at low fields follows the predicted curve for the S =1 quantum chain with energy gap (Δ/ k B ∼10 K) down to near T N . A more definite evidence for the Haldane state is given by studying the effect of the nonmagnetic impurities. We have revealed a real existence of S =1/2 edge states characteristic of the Haldane state and further revealed a crossover from the quantum to classical regimes as a function of both temperature and field. The result is consistent with the model that at low temperatures ( T | J |/ k B ) and high fields ( H > H G ) the system is not in the Haldane state any more.

Field-induced transitions of Y1−xGdx(Co0.93Al0.07)2 in ultrahigh magnetic fields up to 100T

Abstract The magnetization process of Y 1−x Gd x (Co 0.93 Al 0.72 ) 2 with 0 ≤ x ≤ 0.08 has been measured in ultrahigh magnetic fields up to 100 T. A metamagnetic transition to a ferrimagnetic state in a paramagnet with x ≤ 0.06 and a spin-flip transition to a noncollinear state in a ferrimagnet with x = 0.08 have been observed at low temperatures. From the transition fields the exchange constant between Co and Gd can be estimated to be J GdCo = ( −1.78±0.06) ×10 −22 J.

Photoemission study of weakly magnetic Y(Co1-xAlx)2

Abstract We have studied the electronic structure of Y(Co1−xAlx)2 with x = 0.0, 0.12 and 0.18, which compositions cover the paramagnetic, metamagnetic and ferromagnetic phases, by photoemission and inverse-photoemission spectroscopy. The spectra are compared with the density of states given by band-structure calculations. An agreement between experiment and theory was considerably improved by applying a self-energy correction to the band density of states.

59Co NMR study of the metamagnetic transition in Y1−xRxCo3 (R Nd and Gd)

Abstract We have performed 59 Co NMR measurements to study microscopically itinerant metamagnetism in intermetallic compounds Y 1− x R x Co 3 (R  Nd and Gd). At 4.2 K, two metamagnetic transitions induced by the Nd exchange field are found to take place at x ∼ 0.35 and 0.85 in Y 1− x Nd x Co 3 , whereas one transition is observed at x ∼ 0.25 in Y 1− x Gd x Co 3 .

Anomalous magnetic properties due to Co metamagnetism in Ce(Co1−xNix)5

Abstract The magnetization up to 120 T and 10 kbar and magnetostriction up to 40 T have been measured for single-crystalline Ce(Co1−xNix)5 with x ⩽ 0.3. The Co moment is in high moment state for CeCo2 and in low moment state for x ⩽ 0.1. A metamagnetic transition from the low to the high moment state can be induced by applying field up to 120 T for x = 0.1 and 0.2. The relations between the Co moment state and the magnetic characteristics are discussed.

Co metamagnetism and magnetic phase diagram of Y1−xNdxCo3

Abstract AC susceptibility and high field magnetization were measured on oriented powder samples of Y 1− x Nd x Co 3 . The samples exhibit spontaneous and field-induced spin-reorientation transitions, together with two metamagnetic transitions of the Co sublattice. The experimental results suggest that the two metamagnetic transitions occur on different Co sites.