Mitsuhiro Motokawa

Direct observation of the multiple spin gap excitations in two-dimensional dimer system SrCu2(BO3)2

Various spin-gap excitations have been observed in the two-dimensional dimer system SrCu 2 (BO 3 ) 2 by ESR. The zero-field energy gap of the lowest spin-gap excitation shows a splitting into two triplet modes and the energy splitting clearly depends on the magnetic field orientation. A zero-field splitting is also found between the S z =+1 and S z =-1 branches of each triplet. These behaviors are qualitatively explained by considering the anisotropic inter-dimer and intra-dimer exchange couplings. The averaged value of the lowest spin-gap energy is determined to be 722±2 GHz (34.7 K). We have also found a second spin-gap excitation at 1140 GHz (54.7 K), which indicates that the inter-dimer coupling is strong. Besides these modes, a number of gapped ESR absorptions are found and we propose that these excitations are caused by the localized nature of the excited state in the present system.

Magnetotransport properties of (Ga,Mn)As investigated at low temperature and high magnetic field

Abstract Magnetotransport properties of ferromagnetic semiconductor (Ga,Mn)As have been investigated. Measurements at low temperature (50 mK) and high magnetic field ( ⩽27 T ) have been employed in order to determine the hole concentration p=3.5×10 20 cm −3 of a metallic (Ga 0.947 Mn 0.053 )As layer. The analysis of the temperature and magnetic field dependencies of the resistivity in the paramagnetic region was performed using the above value of p , which gave the magnitude of p – d exchange energy |N 0 β|∼1.5 eV .

Submillimeter wave ESR measurements of metamagnetic Y2Cu2O5

Submillimeter wave ESR system in Kobe University is presented. It covers the frequency region from 60 to 383GHz and can apply the pulsed magnetic field up to 30T. The measurement of Y2Cu2O5 single crystals using our system is presented.

Effects of a magnetic field on the growth rate of tetragonal lysozyme crystals

The growth process of tetragonal lysozyme crystals under static and homogeneous magnetic field of 11 T was observed in situ by using an optical microscope which was specially designed and prepared. This optical system, having a spatial resolution of 0.5 μm, was used to measure the growth rate of the lysozyme crystals under 0 and 11 T. The effect of the magnetic field of 11 T was to decrease the growth rate of the crystals. The effect of a magnetic field on the dissolution process of the crystal was also investigated.

Magnetization of Co(SxSe1-x)2 under High Magnetic Field Up to 500 kOe

Proceeding the previous paper (J. Phys. Soc. Jpn. 46 (1979) 1474) the high field magnetization process of Co(S x Se 1- x ) 2 system for 0.70 ≤ x ≤1.00 has been investigated by means of pulse fields up to 500 kOe at fixed temperatures. The metamagnetic behaviors were observed and the phase diagram between the transition field and temperature was given. The saturation moment seemed to disappear at x ≃0.6.

Electron Spin Resonance of Spin-Peierls Material CuGeO3

Magnetization and submillimeter wave ESR measurements have been performed on single crystals of CuGeO 3 using a pulsed high magnetic field. Magnetization jumps are observed at 12.8, 12.5 and 13.5 T for a -, b - and c -axes, respectively, at 4.2 K. The temperature dependences of the linewidth and the integrated intensity of the ESR signal are discussed in connection with the conventional spin-Peierls systems, and the excitation gap against the magnetic field is estimated when the field is applied along the a -axis. ESR has been observed in the magnetic phase above the critical field H c and the g -values have different values from those in the spin-Peierls phase. The origin of this difference is discussed.

EPR and AFMR of Bi2CuO4 in Submillimeter Wave Region

Paramagnetic and antiferromagnetic resonances have been observed for powder samples of Li 2 CuO 2 in submillimeter wave region using pulsed magnetic fields at temperatures from 1.9 K to 265 K. At the paramagnetic state, the g -values have been determined to be g // =2.30 and g ⊥ =2.01. The line-width estimated from the powder signal increases as the frequency increases. Antiferromagnetic resonance modes along the principal axes have been clearly observed even in the powder samples below the Neel temperature and explained by the conventional antiferromagnetic resonance theory. It has been found that the easy axis is parallel to the direction of g // and the anisotropy is almost uniaxial and fairly strong. This fact is quite different from other antiferromagnetic copper oxides. Obtained parameters by AFMR are A =90 mol/emu, A x ′ =0.061 A, A y ′ =-0.021 A, A z ′ =-0.040 A, Γ x ′ =-0.028 A, Γ y ′ =0.018 A and Γ z ′ = 0.010 A.

15 T Cryocooled Nb3Sn Superconducting Magnet with a 52 mm Room Temperature Bore

We succeeded in demonstrating a 15.1 T cryocooled Nb3Sn superconducting magnet with a 52 mm room temperature bore. Two operating currents of 157 A and 90 A for the divided section coils were utilized for the first time in a cryocooled superconducting magnet system. It is found that the current leads are no longer the dominant heat loads because of the use of high-temperature superconductors. In order to realize a high-field cryocooled superconducting magnet comparable to the usual superconducting magnet immersed in liquid helium at 4.2 K, we maintained the coil temperature at a value below 5.0 K during the field sweep in a high magnetic field region.

Containerless Melting of Glass by Magnetic Levitation Method

The Melting of glass materials levitated in high magnetic fields has been carried out without a crucible by using a hybrid magnet and a CO2 laser. A cubic glass with 6 mm sides has become a complete sphere through melting and cooling in the air. This new method will provide opportunities for obtaining high-purity and new heterogeneous materials.

Effect of a magnetic field on the orientation of hen egg-white lysozyme crystals

Recent experiments have shown that lysozyme crystallization in a magnetic field of the order of 1 T can result in a significant degree of orientation of the crystals. We present more extensive experimental results and propose a model to account for this phenomenon. Because of the small susceptibility anisotropy of most protein molecules, the orienting effect is unimportant for smaller aggregates, even those much larger than a critical nucleus. However, during sedimentation crystals grow larger and are more likely to become aligned. The degree of orientation thus depends on crystal growth rate and container geometry, in addition to magnetic field strength, as we have confirmed experimentally.