Sakakibara Toshiro

Evidence of a High-Field Phase in PrV2Al20 in a [100] Magnetic Field

The DC magnetization of a single crystal of cubic PrV2Al20 was examined at very low temperatures down to \({\sim}0.1\) K and in high fields of up to 14.5 T applied along the [100] direction. A fiel...

Anomalous Uniaxial Pressure Effect on the Phase IV Ordering in CexLa1-xB6

We have examined the magnetization M of Ce 0.75 La 0.25 B 6 under uniaxial pressures applied along the [001] direction, focusing our attention on the mysterious phase IV ordering. Magnetization of phase IV, which is nearly isotropic at an ambient pressure, becomes strongly anisotropic at a relatively weak uniaxial pressure of 60 MPa. On entering phase IV from the paramagnetic phase I, M ( T ) increases (decreases) for the field direction H ∥[001] ([110]), suggesting that the order parameter is intrinsically anisotropic. Interestingly, M ( T ) for H ∥[001] exhibits an upward-bending at the ordering temperature T I–IV , and T I–IV ( H ) seems to increase in magnetic field unlike the case of ordinary antiferromagnetic orderings. The results are discussed in view of a spontaneous ordering of an octupole moment in phase IV.

Magnetization Study on the History-Dependent Peak Effect in the Superconducting Mixed State of CeRu2.

A huge peak of irreversible magnetization in CeRu 2 single crystal, together with the equilibrium magnetization, was investigated by means of a static magnetization measurement using a Faraday force magnetometer. The residual resistance ratio of the used crystal exceeds 250, indicating that it is a clean superconductor. Contrary to the previous reports, there is no pinning-free region in the magnetization curves below the upper critical field H c2 . The detailed minor-hysteresis-loop measurement has revealed that the peak structure in the increasing-field magnetization curve around the onset field of the peak strongly depends on previous field-history, resulting in an apparent asymmetry of the peak structure. No trace of paramagnetic suppression of superconductivity in the vortex-penetrated state is observed from the superconducting equilibrium magnetization curves. The peak position, although highly anisotropic, can be interrelated to the peak strength, regardless of the applied field direction. It is li...

Magnetic Correlation in the Ordered Phase of CeOs4Sb12

We performed neutron diffraction and magnetization measurements to reveal the nature of phase transition of a Kondo semiconductor CeOs 4 Sb 12 . Weak antiferromagnetic (AFM) reflections characterized by a wave vector q = (1 0 0) were observed, and the ordered moment value is around 0.07µ B /Ce at zero magnetic field. The AFM structure is rapidly suppressed by magnetic field of 1 T, in contrast to the transition temperature suggested to be enhanced by magnetic field. Only ferromagnetic correlation is observed above 1 T. Such drastic variation of the magnetic correlation is closely connected into the transport properties; the AFM ordered phase below 1 T and the induced ferromagnetic state above 1 T correspond to the semiconducting and metallic states, respectively.

Structural, Magnetic, and Superconducting Properties of Caged Compounds ROs2Zn20 (R = La, Ce, Pr, and Nd)

The electrical resistivity, magnetization, and specific heat of the caged compounds ROs2Zn20 (R = La, Ce, Pr, and Nd) have been measured to study their structural, magnetic, and superconducting properties. These measurements indicate that the compounds undergo structural transitions at Ts = 151, 109, 87, and 62 K, respectively. The decrease in Ts along with the lanthanoid contraction suggests that the high-temperature phase is more stable for a smaller lattice volume. Analysis of the lattice specific heat of LaOs2Zn20 reveals that the Zn atom at the 16c site encapsulated in the R2Zn12 cage vibrates at a low energy of 3 meV. For CeOs2Zn20, the small magnetic susceptibility with a broad maximum indicates the valence-fluctuating state of the Ce ions. In PrOs2Zn20, the crystalline electric field ground state of the 4f2 state of the Pr3+ ion remains in a non-Kramers doublet at T > Ts, which is lifted by symmetry lowering of the Pr site at T < Ts. Thereby, the quadrupolar degrees of freedom are quenched, avoidi...

Anisotropic spin-glass and cluster-glass of layered FexTiS2 crystals

Zero-field cooled (ZFC) and field cooled (FC) magnetizations have been measured on the spin- and cluster-glasses of iron intercalation compound Fe x TiS 2 ( x =0.1-1/3) over the temperature range 4.2-150 K. We have found appreciable field cooling effects in both spin- and cluster-glass phases. From the observed ZFC and FC curves, strong anisotropies in the paramagnetic Curie temperature and effective magnetic moments are found, for which a qualitative discussion is given.

Verification of Anisotropic s-Wave Superconducting Gap Structure in CeRu2 from Low-Temperature Field-Angle-Resolved Specific Heat Measurements

The field-angle-resolved specific heat C(T,H,φ) of the \(f\)-electron superconductor CeRu2 (\(T_{\text{c}}=6.3\) K) has been measured at low temperatures down to 90 mK on two single crystals of slightly different qualities. We reveal that the C(φ) oscillation in a rotating magnetic field, originating from the gap anisotropy, diminishes at low temperatures below the characteristic field \(H^{\ast}\), as expected for an anisotropic gap without nodes. We also observe the suppression of \(H^{\ast}\) by decreasing the gap anisotropy ratio Δmin/Δmax, a behavior that has been predicted from a microscopic theory for anisotropic \(s\)-wave superconductors. The present technique is established as a powerful tool for investigating minimum-gap structures as well as nodal structures.The field-angle-resolved specific heat C(T,H, φ) of the f -electron superconductor CeRu 2 (Tc = 6.3 K) has been measured at low temperatures down to 90 mK on two sing le crystals of slightly di fferent qualities. We reveal that the C(φ) oscillation in a rotating magnetic field, originating from the gap anisotropy, diminishes at low temperatures below the characteristic fie ld H∗, as expected for an anisotropic gap without nodes. We also observe the suppression of H∗ by decreasing the gap anisotropy ratio ∆min/∆max, a behavior that has been predicted from a microscopic theory f or anisotropics-wave superconductors. The present technique is established as a powerful tool for inve stigating minimum-gap structures as well as nodal structures.

Anomalous Field-Angle Dependence of the Specific Heat of Heavy-Fermion Superconductor UPt3

We have investigated the field-angle variation of the specific heat C(H, phi, theta) of the heavy-fermion superconductor UPt3 at low temperatures T down to 50 mK, where phi and theta denote the azimuthal and polar angles of the magnetic field H, respectively. For T = 88 mK, C(H, theta=90) increases proportionally to H^{1/2} up to nearly the upper critical field Hc2, indicating the presence of line nodes. By contrast, C(H, theta=0) deviates upward from the H^{1/2} dependence for (H/Hc2)^{1/2} > 0.5. This behavior can be related to the suppression of Hc2 along the c direction, whose origin has not been resolved yet. Our data show that the unusual Hc2 limit becomes marked only when theta is smaller than 30. In order to explore the possible vertical line nodes in the gap structure, we measured the phi dependence of C in wide T and H ranges. However, we did not observe any in-plane angular oscillation of C within the accuracy of dC/C~0.5%. This result implies that field-induced excitations of the heavy quasiparticles occur isotropically with respect to phi, which is apparently contrary to the recent finding of a twofold thermal-conductivity oscillation.

Low Energy Excitations in the Mixed State of the Anisotropic s-Wave Superconductor CeRu2

Angle-resolved specific heat measurements are preformed on the f -electron superconductor CeRu 2 in rotating magnetic fields 0.5≤ H ≤6 T at various temperatures 0.3≤ T ≤2 K. In the whole H – T rang...It has been clarified that bulk superconductivity in Fe

Magnetic Phase Diagram of Pr1-xLaxFe4P12 (0 ≤x ≤0.15)

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