Hiroko Aruga Katori

Magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid

Abstract Magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid having one-dimensional micropores are studied. O2 is well known as a magnetic molecule with S=1. In the case of the low adsorption, temperature dependence of the susceptibility shows the Schottky-type broad peak and the high-field magnetization process has a step at around 34T with saturation moment of 2 μ B/O2. These results are interpreted by the dimer model of S=½ with an antiferromagnetic exchange interaction. Broadening of the step of magnetization with increasing the adsorption may be due to the inter-dimer interaction or the distribution of the intra-dimer exchange interaction. Linear magnetization process which is characteristic of one-dimensional Heisenberg antiferromagnet has not been observed even in the full pore region.

Generation of 500 T fields by electromagnetic flux compression and their application to cyclotron resonance experiments

Abstract Magnetic fields higher than 500 T were generated by means of electromagnetic flux compression. They were applied to cyclotron resonance experiments for bulk GaAs and two-dimensional (2D) elecron systems in GaAs/AlGaAs quantum wells using a CO laser (5.527 μm). A large spin splitting was observed in 2D electron systems even for a carrier concentration higher than n = 10 11 cm −2 . The dependence of the effective mass and the spin splitting on carrier concentration was studied.

Magnetic phase diagram of the triangular lattice antiferromagnet ABX3 under high magnetic field

Our recent experimental study on the magnetic phase diagrams of stacked triangular lattice antiferromagnets (TAL-AF) is summarized. The precise magnetization measurements in the temperature range between 1.4 and 20 K under static magnetic fields up to 12 T have revealed that the magnetic field versus temperature phase diagrams of the ABX3 compounds are classified into two types depending on the difference in their magnetic anisotropies in agreement with the theoretical prediction. In the case of the XY TAL-AF, CsMnBr3 and RbMnBr3 with an easy plane anisotropy, only a single transition is observed at zero field but it splits into two successive transitions under finite fields in the basal plane. On the other hand, in the case of the Ising-like TAL-AF, CsNiBr3 and CsMnI3 with an easy axis anisotropy, two successive transitions are observed at zero field and these are merged into a single transition at the multicritical point under finite fields parallel to the c-axis and a line of the spin-flop transition also meets this point.

Electronic structure of metal hydrides studied by high field magnetization

Abstract The influence of hydrogen on the electronic structure of an intermetallic compound has been studied from magnetization measurements in ultrahigh magnetic fields up to 130 T for a prototype system YCo 3 H x . The dependence of the magnetic moment on hydrogen content and magnetic field lead to the following conclusions. The general structure of the density of states (DOS) in the upper part of the 3d band is still maintained in the hydride, but the curvature of the DOS curve is slightly modified in the β phase x = 1.0–1.9), and more strongly modified in the γ phase ( x = 3.2–4.0). The modification of the DOS is related to the occupation sites of hydrogen. The electronic population in the 3d band is hardly changed upon hydrogenation, and it is about +0.1 electron Co −1 per absorbed hydrogen atom. The electrons originating from hydrogen atoms are almost contained in the metal-hydrogen bonding band. The rest of them occupy the 3d band, causing the Fermi level to shift slightly upwards.

Magnetic properties of the hydrides based on RFe compounds

Abstract The influence of hydrogenation on the magnetic properties of the compounds GdFe 3 , Gd 6 Fe 23 , DyFe 3 and Dy 6 Fe 23 has been investigated by measurements of powder high field magnetization at 4.2 K in pulsed fields up to 38 T. The magnetization curves of the hydrides GdFe 3 H x and Gd 6 Fe 23 H x show the spin-flip transition from the ferrimagnetic state to a noncollinear spin structure at the critical field B c . The exchange coupling n RT between the R and the Fe sublattices was estimated from the slope dM/dBabove B c . The values of n RT , B c and the compensation temperature T comp decrease with increasing hydrogen composition, indicating a weakening in the R T coupling. The magnetization of the hydrides DyFe 3 H x and Dy 6 Fe 23 H x does not reach saturation even at 38 T. In the Dy hydrides the magnetocrystalline anisotropy for the Dy ion competes with n RT which is weakened upon hydrogenation. The fanning effect is revealed by the Dy moments at the ground state of Dy 6 Fe 23 H 12 . The Fe moment increases in the initial stages of absorption of hydrogen and then decreases as more hydrogen is absorbed.

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.

Metamagnetic transition of the reentrant spin-glass Fe0.65 Mn0.35TiO3: Anomalous dependence on sweep-rate of magnetic fields

Abstract The magnetization processes of the reentrant spin-glass Fe0.65Mn0.35TiO3 have been observed in magnetic fields with various sweep-rates by using a pulse magnet, a superconducting magnet and a water-cooled Bitter-type magnet. It has been found that there exists an essential difference between the magnetization processes in the sweep-rate regions ∼103T/s (pulse magnet) and ≤0.75T/s (superconducting and Bitter-type magnets). The diffeerence is considered to be due to the spin structure of a spin-glass state.

Faraday rotation and magnetization measurements of FexMn1−xF2 in megagauss fields

Abstract Measurements of Faraday rotation and magnetization have been performed on antiferromagnetic FeF 2 , MnF 2 and their mixtures in high magnetic fields above 100 T using a single turn coil method. Faraday rotation shows the component of magnetization contributed only by Fe moments in the mixed crystals, while the total induced magnetization is obtained by magnetization measurements.

Magnetic Energy Gap in the Crystal of an Organic Biradical, m-BNN: m-Phenylene Bis(α-Nitronyl Nitroxide)

Abstract A novel phase transition is observed in the crystal of a triplet (S=l) biradical, m-BNN. The crystal is composed of equivalent dimers of the biradicals at room temperature. From susceptibility, high-field magnetization and X-ray diffraction at low temperatures, it is shown that below about 10 K imperfect cancellation of magnetic moment occurs between antiferromagnetically coupled S=1spins only in half the number of dimers in the crystal.

Spin flop transition of the diluted antiferromagnet MnxMg1−xTiO3☆

Magnetization measurements were made for the diluted antiferromagnet MnxMg1−xTiO3 up to high-field region. The critical field of the spin-flop-like transition HSF approaches zero at x ∼ 0.6 and the magnetization curve becomes not to depend on directions of the applied field indicating that the x ≤ 0.6 samples are magnetically isotropic. It is considered that the critical concentration of x ∼ 0.6 giving HSF = 0 is connected with the crossover phenomenon from random-field behavior to spin-glass behavior observed around x = 0.6. A small but anomalous hysteresis is observed at the spin-flop-like transition of MnxMg1−xTiO3 (x <1.0). This hysteresis is attributed to the random-field effect.