Shinhachiro Saito

Antiferromagnetism in Cu(NH3)4SO4·H2O

The magnetic structure of the magnetic linear chain substance, Cu(NH 3 ) 4 SO 4 ·H 2 O, has been investigated by means of proton nuclear magnetic resonance and magnetic susceptibility measurements. A transition from the short range (or intra-chain) ordered state to the long range ordered state was found at 0.43±0.01°K in both measurements. The magnetic spin arrangement inferred from the rotation studies of the proton N. M. R. is nearly antiferromagnetic in a –O–Cu–O–Cu–O– chain, and nearly parallel to the c -axis. It is plausible that spins cant by few degrees from the direction parallel to the c -axis. This spin structure is inconsistent with the previous magnetic susceptibility data by Haseda and Miedema. Therefore, susceptibility measurements have been repeated taking care of the thermal equilibrium between the sample and the cooling agent in the temperature region between 4.25 and 0.03°K, and the results different from their work have been obtained, which are not inconsistent with the spin structure i...

Development of advanced high field superconductors

Abstract Recent improvements and developmental research on several high field superconducting wires are reviewed. High field characteristics of NbTiHf wires, wound in a 13.08 T superconducting magnet in a 1.8 K pressurized superfluid helium bath, have been studied in detail. Ti-alloyed Nb 3 Sn fm wires prepared by the Nb-tube method showed excellent high field J c -characteristics and were wound in a 16.7 T superconducting magnet. One of these wires was employed in the HOMER facility (a multipurpose superconducting magnet at KfK) and generated 20.15 T, recently. A new process called the clad chip extrusion (CCE) method has been developed for the preparation of superconducting Nb 3 Al wires. Short samples of the CCE processed Nb 3 Al wires showed J c higher than 10 4 A/cm 2 up to 18.8 T at 4.2 K. One of the in-situ processed V 3 Ga short sample wires prepared by an induction melting using a CaO crucible showed J c =10 4 A/cm 2 at 16.2 T and 4.2 K, which will be improved by further optimization of the process and the composition.

Long range ordering of a linear-chain Heisenberg antiferromagnet, tanol, below 1 K

Abstract Magnetization of TANOL (4-hydroxy-2, 2, 6, 6-tetramethylpiperidinoxy) has been measured with the proton NMR method below 1 K. The antiferromagnetic transition temperature T N is determined to be 0.49 ± 0.01 K under an external magnetic field of 1.6 kOe, which is in good agreement with the value obtained by Boucher et al. from a heat capacity measurement. The reason of the discrepancy between this value and the previously reported one is discussed. The sublattice magnetization as a function of temperature, M ( T ), is represented by (1 − 0.729 T 2 ) in the region below 0.35 K. Critical index of the magnetization, β, is estimated to be 0.335 ± 0.02.

Magnetic susceptibility of a linear chain antiferromagnet, TANOL, at very low temperatures

Abstract The magnetic susceptibility of powdered crystals of TANOL (4-hydroxy-2,2,6,6-tetramethylpiperidinol-1-oxy) has been measured in the temperature range between 4.2 and 0.1 K. The results are compared with the theoretical calculations of Bonner and Fisher. Below 0.43 K, an interesting thermal behavior has been observed, which is thought to be associated with a first order phase transition. T N is estimated to be 0.34 K from the thermal behavior of the sample.

Proton Nuclear Magnetic Resonance in Cu(NH3)4SO4·H2O at Very Low Temperatures

Proton nuclear magnetic resonance study of copper tetramin-sulphate monohydrate (Cu(NH 3 ) 4 SO 4 ·H 2 O) has been done between 0.25 and 4.2°K. In the paramagnetic state, resonance lines were assigned to protons in NH 3 or in H 2 O group and the positions of the protons in the both groups were estimated. A drastic change in the resonance signal, which is due to the transition from the short range ordered state to the long range ordered state, is observed at 0.42±0.05°K with H 0 applied in the be plane. Below 0.42°K, the angular dependence of the resonance signal has a period of 360°. From the rotation study, it is inferred that Cu 2+ magnetic moments are nearly mutually antiparallel and along the -O-Cu-O- chains. On the other hand, there is a broad intense resonance line at a frequency of the free proton, which is independent of the direction of the external static field.

Temperature inhomogeneity in the glass mixing chamber of a 3He/4He dilution refrigerator

The temperature inhomogeneity in the glass mixing chamber of a (3)He/(4)He dilution refrigerator has been studied. The inhomogeneity is reduced to 10 mK by inserting a cylindrical spacer in the mixing chamber.

Kapitza resistance and thermal conductivity of Mn(NH4)2 Tutton salt

Abstract Thermal boundary resistance, R B , between liquid 3 He and Mn(NH 4 ) 2 Tutton salt is measured by the dc method in the temperature region 0.09 to 0.5 K. Thermal conductivity, K , of this salt is also measured in the region near the Neel temperature, T N = 0.176 K . The temperature dependence of K varies beyond T N , but no characteristic change in the slope of R B is observed throughout the ordering region. Standing on the experimental evidences, a caution for a use of the thermal relaxation method in R B measurements is given in this paper.