M. Motokawa

Submillimeter EPR of Co:Rb2MgF4 and anomalous g-values

We found new effect which changes g-values of pair and trimer Co2+ spins by EPR of Rb2Co0.3Mg0.7F4 at 220, 370, 762.2 and 693.6 GHz in pulsed high magnetic fields. The anomalous g-values come from mixing of 1LS and strong exchange interaction.

Magnetization and Magnetoresistance of Fe/Gd Ferrimagnetic Multilayer Films

Spin-flop and compensation phenomena of the magnetization in ferrimagnetic Fe/Gd multilayer films have extensively been investigated. It turns out that experimental results of the field and temperature dependence of magnetization agree fairly well with the calculated ones based on the molecular field model. In the calculation, we have obtained the magnetic structure, assuming that the composition is modulated stepwise, and that the exchange interactions in Fe and Gd layers are the same values as those in bulk Fe and Gd metals, respectively. Both longitudinal and transverse magnetoresistances show a crossover near the spin flop field due to the change in the magnetic structure. This crossover behavior is qualitatively well simulated by the calculation on the assumption of the parallel current flow in each atomic layer.

Gap state of SmB6

Abstract We performed optical reflectance and transmission measurements on SmB6 and their temperature dependence. At low temperature where the gap was formed, two peak structures were resolved at 0.1–0.5 eV in the optical conductivity spectrum (σ). Such structures are discussed in relation to the gap state.

Production of repeating pulsed high magnetic field

Abstract Pulsed high magnetic fields up to 20T with a duration of 1 ms are repeated 20 000 times with a duty cycle of 0.5 Hz. The magnet is a water cooled Bitter type composed of copper and FRP disks stacked in turn. This will be useful to increase the S/N ratio of physical experiments, expecially when used with other equipment operated in pulsed mode.

Influence of silver on critical current of the Y–Ba–Cu–O superconductor

Electrical properties of Y--Ba--Cu--O superconductors, such as the critical current density and the zero-resistance temperature, are systematically improved by changing the compression pressure during the formation process of the specimens. Also, by changing the silver powder content of the superconducting Y--Ba--Cu--O powder, the critical current density and the zero-resistance temperature are remarkably improved. The resistance-drop temperature is insensitive to changes in the compression pressure, silver content, and magnetic field, whether the field is applied perpendicular to the specimens. The critical current density of the specimens with and without silver decreases exponentially with the perpendicular magnetic field. The critical current densities of specimens without silver showed much lower sensitivity to perpendicularly applied magnetic fields than those of the specimens having a silver content. Along with the above improvements, the present paper also examines several factors that affect the superconducting characteristics. These factors include impurities in the air and strong magnetic fields.

An idea for the easy construction of a high field magnet

Abstract A new method for the easy construction of a pulsed field magnet is developed. Alumina powder with ice is used as a reinforcement spacer in a stainless steel shell. Magnetic fields up to 35 T have been produced at liquid N2 temperature by a 23.4-kJ capacitor bank.

Neutron diffraction of CsCuCl3 in high fields

Abstract Neutron diffraction measurements of triangular lattice CsCuCl 3 have been performed in a pulsed high magnetic field up to 14T. For an applied field parallel to the c -axis and below B c = 10T at 7 K, Bragg reflection is observed at (1/3 1/3 0.085) showing a long period helical spin alignment along the c -axis and a triangular umbrella-like structure in the c -plane. The intensity of this reflection drastically changes at B c and a new reflection at (1/3 1/3 0) appears. These results well explain a new type of magnetic phase transition which cannot be understood by the classical theory. When B is perpendicular to the c -axis more complicated results are observed.

Metamagnetic transition in Y2Cu2O5

Two successive metamagnetic transitions have been observed in single crystals of Y 2 Cu 2 O 5 at B c1 = 3.0 T and B c2 = 4.8 T for B∥b-axis, above which the magnetization gradually increases and saturates at B s = 7.2 T. The most interesting point in this study is that the metamagnetic transition has not been supposed in the Cu 2+ spin system due to the small anisotropy and never observed in copper compounds so far

High field ESR of R2Cu2O5 (R=Y, Lu, Sc, In)

Abstract Submillimeter wave ESR measurements of R 2 Cu 2 O 5 (R=Y, Lu, Sc and In) powder samples have been performed for the frequency range from 90 to 380 GHz and for the temperature range from 1.8 to 265K using the pulsed magnetic field up to 16T. The g -values and the line width are obtained from the results of EPR absorption. Below T N , the changes of the ESR modes have been observed at the magnetic fields corresponding to the metamagnetic transitions observed in the magnetization measurements.

ESR measurements of CsCuCl3 in high field phase

Abstract Submillimeter wave ESR measurements of CsCuCl3 have been performed at temperatures below TN = 10.5 K for H/c and H⊥c. For H/c a change of the ESR mode has been observed at a magnetic field around 12T, which corresponds to the field where a small magnetization jump occurs and it was interpreted as a quantum-fluctuation-induced magnetic phase transition proposed by Shiba and Nikuni. For H⊥c small absorption lines have been observed around 10 T together with the main absorption lines. These results will be discussed in connection with our calculated result and magnetization and neutron diffraction measurements.