Kazuyoshi Yoshimura

Itinerant electron metamagnetism in Y(Co1−xAlx)2

Abstract Magnetization measurements on the itinerant electron magnet Y(Co 1−x Al x ) 2 up to 350 kOe have clearly revealed metamagnetic transitions in the paramagnetic region (0.07⩽ x ⩽0.11). The transition is sharp for low x , suggesting itinerant electron metamagnetism to exist in YCo 2 at 1 MOe, while it is broadened and disappears upon the onset of ferromagnetism at x ∼0.13.

Cu spin dynamics in high Tc and relaxed oxides investigated by nuclear spin-lattice relaxation.

Abstract Temperature and concentration dependences of Cu spin dynamics have been investigated for high T c and related metallic oxides by the measurements of 63 Cu nuclear spin-lattice relaxation rates. The results suggest the gap opening in the Cu d-spin excitation spectrum at around 120 K, follwed by superconducting transition.

Itinerant electron metamagnetism and spin fluctuations in nearly ferromagnetic metals Y(Co1-xAlx)2

High-field magnetisation- and temperature-dependent susceptibility of Laves phase inter-metallic compounds Y(Co1-xAlx)2 are investigated in the strongly exchange-enhanced paramagnetic region (0<or=x<or=0.11) in pulsed magnetic fields up to 100 T. In the whole concentration range, a sharp metamagnetic transition is observed in the low-temperature magnetisation process, while the low-field susceptibility exhibits a maximum at finite temperatures. The transition field Bc and the temperature of the susceptibility maximum Tmax obtained as a function of x indicate a linear relationship, i.e. Bc/Tmax=constant. The result clearly suggests that the susceptibility maximum of the nearly ferromagnetic metals is strongly correlated with itinerant electron metamagnetism.

High field magnetization of the Laves phase compounds M(Co1−xAlx)2 (M = Y, Lu)

Abstract Magnetization measurements have been carried out on the Laves phase compounds M(Co 1− x Al x ) 2 (M = Y, Lu) up to 42 T. Sharp metamagnetic transitions with small hysteresis are found in Y(Co 1− x Al x ) 2 , while broad transitions with large hysteresis are found in Lu(Co 1− x Al x ) 2 . The results suggest that the former compounds are magnetically homogeneous but the latter inhomogenous.

Preparation and properties of SiO2-TiO2 thin films from silicic acid and titanium tetrachloride

The preparation of SiO2-TiO2 thin films by the sol-gel method using silicic acid and titanium tetrachloride as starting materials was studied. The homogeneous sols were obtained by the condensation reaction of silicic acid with titanium tetrachloride in methanol-tetrahydrofuran. The dipcoating of slide glasses and silicon wafers followed by heat treatment gave oxide thin films of 88–93% transmittance, 3000–4500 Å thickness, and 1.45–1.80 refractive index, depending on heat-treatment temperature and TiO2 content. FT-IR measurement showed that the Si-O-Ti bond is formed even in the sol and films. The variations of film thickness and refractive index on transformation from the gels into the oxides were found to be quite low.

NMR study of nearly itinerant antiferromagnetic Y1−xScxMn2

Abstract The NMR investigation of Y 0.97 Sc 0.03 Mn 2 has revealed that this compound remains paramagnetic down to 4.2 K. The nuclear spin-lattice relaxation rates, 1/ T 1 , of 55 Mn and 45 Sc in Y 0.97 Sc 0.03 Mn 2 show the T 1 2 dependence as predicted from the self-consistent renormalization (SCR) theory of spin fluctuations for nearly antiferromagnetic metals.

Itinerant metamagnetic transition in Y(Co1−xFex)2

Abstract High field magnetization measurements have been performed to examine the existence of itinerant metamagnetism in exchange-enhanced systems related to YCo2 together with Fe1−x CoxSi. In the Y(Co−xFex)2 system, the meta magnetism inherent in YCo2 has been observed in 0.04 ⩽x⩽0.07. The transition is not as sharp as in the Y(Co1−xAlx)2 system. Other exchange-enhanced paramagnets Y(Co−xCux)2 and Y1−xLaxCox2 and weakly itinerant ferromagnet Fe1−xCoxSi exhibit no metamagnetic transition up to 430 kOe.

Spin fluctuations in weakly itinerant ferromagnets Y(Co1−xAlx)2

Abstract The nuclear spin-lattice relaxation rate, 1/ T 1 , has been measured in weak itinerant ferromagnets Y(Co 1− x Al x ) 2 . The temperature and magnetic field dependence of 1/ T 1 T has been found to be well described by the self-consistent renormalization (SCR) theory of spin fluctuations. The parameters characterizing spin fluctuations in this system were estimated from NMR and magnetic measurements. The temperature dependence of susceptibility calculated from these parameters well reproduces the experimental results.

NMR study of itinerant antiferromagnet YMn12

Nuclear magnetic resonance and relaxation (NMR) were measured for 55 Mn in the itinerant antiferromagnet YMn 12 . In spite of its small Mn moments, the Heisenberg model with S = 1/2 gives a better understanding of the temperature dependence of the resonance frequency v res rather than the SCR theory for weak antiferromagnets, suggesting an intermediate regime of metallic antiferromagnetism in YMn 12 . The behavior of 1/ T 1 can be explained qualitatively by both the SCR theory and the localized moment model.

Possible spin singlet quadrumerization in Pb2Re2O7−δ

A single crystal of pyrochlore Pb(2)Re(2)O(6.75) was prepared by hydrothermal synthesis, and its magnetic and transport properties were investigated. Pb(2)Re(2)O(6.75) shows the metallic conduction with an anomalous second-order structural phase transition at T(s)=294 K, in which the magnetization and the structure change similarly to that at 200 K of the superconductor Cd(2)Re(2)O(7). A three-dimensional Ising-like order parameter probed by the atomic displacement suggests that an unconventional spin singlet state is possibly realized in the ground state of Pb(2)Re(2)O(6.75), in which four spins make a quadrumer in order to remove the spin frustration of the pyrochlore lattice.