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

通过磁化强度和比热测量研究了磁场对立方相PrPb_3中AFQ相的影响。结果表明，磁场使AFQ转变温度TQ（H=0时=0.4 K）显著升高。这一行为很好地解释了反铁磁（AF）之间的相互作用，在AFQ阶段的场致交错磁矩。在平行于[110]方向施加0.1GPa的单轴压力下，研究了Ce_（0.75）La_（0.25）B_6中第IV相的磁性。第四相的磁化率在零压力下是各向同性的，在单轴压力下变得显著的各向异性。在TmTe中，磁化率随温度的升高而急剧增加，在TN=0.22 μ K处出现AF转变，磁化率出现发散。结果表明，铁磁力矩是由交替的各向异性，由于预先存在的AFQ秩序在TQ=1.8 K的AF阶段诱导。当AF态和AFQ态用同一波矢描述时，这是可能的，这与最近的中子衍射研究相一致。我们研究了URu_2Si_2超导混合态的顺磁效应。结果表明，当温度低于Tc时，G-L参数κ2减小，表明该对为单重态。在该体系中实现了d波超导，并通过磁化强度测量研究了CeRu_2的峰值效应。在混合状态的磁化曲线中没有观察到一阶转变的痕迹，也没有观察到顺磁效应的任何证据，从而拒绝了向FFLO状态的相变的可能性。在这个系统中的峰值效应是相当好地解释了同步效应。

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.