Very Low-Temperature Magnetization Measurements on the Electron Systems with Low Characteristic Temperature

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Effect of magnetic field on the AFQ phase in the cubic compound PrPb3 has been studied by means of magnetization and specific heat measurements. It is found that the AFQ transition temperature TQ (=0.4〜K at H=0) remarkably increases in magnetic field. This behavior is well explained by antiferromagnetic (AF) interactions between the field-induced staggered magnetic moment in the AFQ phase. Analysis of the observed anisotropy TQ(H//[100]>TQ(H//[110]), however, strongly suggests the presence of a weak ferro-octupolar interaction.Magnetic properties of the phase IV in Ce0.75La0.25B6 have been studied under uniaxial pressure of 0.lGPa applied parallel to the [110] direction. The magnetic susceptibility of phase IV, which is isotropic at zero pressure, becomes remarkably anisotropic under the uniaxial pressure. Magnetic state of phase IV is found to be quite sensitive to the uniaxial strain.In TmTe, magnetic susceptibility increases enormously on cooling and appears to diverge upon an AF transition at TN=0.22〜K. The results imply that a ferromagnetic moment is induced in the AF phase by an alternating anisotropy due to the preexisting AFQ order at TQ=1.8〜K. This is possible when both AF and AFQ states are described by the same wave vector, in agreement with recent neutron diffraction studies.Paramagnetic effect in the superconducting mixed state of URu2Si2 has been studied. It is found that the G-L parameter κ2 decreases on cooling below Tc, suggesting that the pairing is a singlet. A d-wave superconductivity is considered to be realized in this system.The peak effect in CeRu2 has been studied by means of magnetization measurement. No trace of a first order transition nor any evidence of a paramagnetic effect is observed in the magnetization curves of the mixed state, rejecting a possibility of a phase transition to the FFLO state. The peak effect in this system is rather well explained by a synchronization effect.