Hagiwara Masayuki

Magnetic Properties of Single Crystalline RCu2Si2 (R: Rare Earth)

A series of ternary compounds RCu 2 Si 2 (R: rare earth) has been grown in single-crystalline form by the flux method. The magnetic properties of these compounds were investigated by measuring the lattice parameter, electrical resistivity, magnetic susceptibility, and magnetization. All the compounds crystallize in the tetragonal ThCr 2 Si 2 -type structure. Most of these compounds order antiferromagnetically at low temperatures, except when R=Y, La, Yb, and Lu. The magnetic anisotropy in the susceptibility and magnetization at low temperatures is found to be relatively small despite the tetragonal crystal structure. An increase in the electrical resistivity just below the ordering temperature and a first-order-like transition are characteristic features of RCu 2 Si 2 with R = light rare earth and R = heavy rare earth, respectively.

Field-Induced Quadrupolar Ordered Phase for H∥ in Heavy-Fermion Compound YbCo2Zn20

Magnetic susceptibility, high-field magnetization up to 500 kOe, and specific heat in a wide temperature range from 0.06 to 300 K were measured for single crystals of the cubic heavy-fermion compound YbCo 2 Zn 20 in order to elucidate the electronic states of the compound at low temperatures. A strong increase in the magnetic specific heat in the form of C mag / T below ∼1 K is approximately explained by the resonant level model for S = 1/2 with the Kondo temperature T K = 1 K, and an extremely large C mag / T ≃8 J/(K 2 ·mol) below about 0.2 K is explained by considering the magnetic entropy of the doublet ground state in the 4 f crystalline electric field (CEF) scheme of an Yb 3+ ion, which corresponds to an extremely large electronic specific heat coefficient. The field-induced ordered phase for H ∥ , which has recently been found by low-temperature magnetization measurements, was precisely studied by electrical resistivity and specific heat measurements, and was observed in a limited angular range ...

Electrical and Magnetic Properties of CeAu2Si2

We succeeded in growing a high-quality single-crystal of CeAu 2 Si 2 , which was previously reported to be highly sample-dependent in terms of electrical and magnetic properties. CeAu 2 Si 2 is not a simple AF1-type antiferromagnet, but reveals three antiferromagnetic transitions in a narrow temperature range from the Neel temperature T N1 =9.6 K to T N3 =8.0 K. A clear metamagnetic transition with two steps was observed at H c1 =53 kOe and H c2 =55 kOe in the magnetization curve below 5 K for the magnetic field along an antiferromagnetic easy-axis, namely, the tetragonal [001] direction, with a saturation moment of 1.53 µ B /Ce. The magnetic susceptibility and magnetization are anisotropic, which are well explained by results of crystalline electric field analyses. We also studied the de Haas–van Alphen (dHvA) effect. The detected dHvA branches are found to be consistent with those of a non-4 f reference compound such as YCu 2 Si 2 .

Anisotropic Magnetic Properties of a Pressure-induced Superconductor Ce2Ni3Ge5

Single crystals of a pressure-induced superconductor Ce 2 Ni 3 Ge 5 have been successfully grown by the flux method. The anisotropic magnetic properties due to the orthorhombic crystal structure have been studied precisely by the electrical resistivity, specific heat, magnetic susceptibility, and high-field magnetization measurements. The results of these measurements confirmed two antiferromagnetic transitions at T N1 =5.0 K and T N2 =4.3 K. The electronic specific heat coefficient obtained from the low-temperature specific heat data amounts to 90 mJ/K 2 ·mol Ce. The high-field magnetization for H ∥[100] shows four magnetic transitions at 11.8, 12.9, 17.5 and 23.9 T with a saturation moment of 0.73 µ B /Ce at 1.3 K. On the other hand, two magnetic transitions are observed for H ∥[010] and [001], with saturation moments of 0.43 and 1.1 µ B /Ce, respectively. We have also performed the crystalline electric field (CEF) analysis on the magnetic susceptibility and magnetization to understand the magnetocrysta...

Unusual Magnetic State with Dual Magnetic Excitations in the Single Crystal of S = 1/2 Kagome Lattice Antiferromagnet CaCu3(OH)6Cl2 ∙ 0.6H2O

We have succeeded in preparing single crystals of CaCu3(OH)6Cl2 ∙ 0.6H2O, a candidate for the S = 1/2 Kagome lattice antiferromagnet. Magnetic properties of the compound are dominated by the nearest neighbor antiferromagnetic interaction J1, and the next nearest neighbor ferromagnetic J2 and an antiferromagnetic Jd across a hexagon, which is different from related compounds Kapellasite and Haydeeite with ferromagnetic J1. Magnetic susceptibility exhibits a sudden increase below 13 K and a cusp anomaly at T* = 7.2 K in the ab-plane, whereas only a moderate enhancement is observed below T* along the c-axis. A tiny peak detected in heat capacity at T* indicates the occurrence of a magnetic phase transition. The low temperature magnetic heat capacity was reproduced by assuming a two-dimensional spin-wave component and a temperature-linear term. The spin-wave contribution suggests a magnon excitation in a short-range ordered region, whereas the relatively large T-linear term 5.9 mJ/(Cu-mol·K2) at H = 0 T of th...

Collapse of Magnetic Order of the Quasi One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8 in Transverse Fields

We have performed magnetization measurements of the quasi one-dimensional (1D) \(S = 1/2\) Ising-like anti ferromagnet BaCo2V2O8 in transverse fields. Different from the expectation by the 1D \(S = 1/2\) \(XXZ\) model, a steep suppression of the antiferromagnetic order is observed for \(H\parallel[100]\), whereas the experimental results for \(H\parallel[110]\) agree with the \(XXZ\) model. We show that these anisotropic behaviors are caused by a characteristic screw chain structure in BaCo2V2O8, which gives rise to a peculiar angular dependence of effective fields upon application of uniform external magnetic fields.

Electronic and Magnetic Properties in Heavy Fermion Ferromagnet YbPdGe

The crystal structure of YbPdGe is orthorhombic, with a large lattice constant for the b -axis. Reflecting this crystal structure, the electronic state is well conductive in the a – c plane. Magnetically YbPdGe is a ferromagnet with a Curie temperature T C = 11.4 K, and ferromagnetic moments are most likely oriented along the b -axis. The electronic specific heat coefficient γ=150 mJ/(K 2 ·mol) and a reduced magnetic entropy at T C suggest that YbPdGe is a heavy fermion ferromagnet.

Multiple Metamagnetic Transitions in Antiferromagnet Yb2Pt2Pb with the Shastry–Sutherland Lattice

From the magnetization and magnetoresistance measurements, we constructed the magnetic phase diagram of Yb 2 Pt 2 Pb with the Shastry–Sutherland lattice, which consists of characteristic two phases below 1 K with many metamagnetic transitions, revealing magnetic frustrations.

Characteristic High-Field Magnetization in a Transuranium Antiferromagnet NpRhGa5

We have measured the high-field magnetization for a transuranium antiferromagnet NpRhGa 5 with two successive antiferromagnetic transition temperatures of T N1 =36 and T N2 =32 K and an ordered moment of 0.96 µ B /Np. For the magnetic field along the easy-axis of the [100] direction of the tetragonal structure, the magnetization indicates a metamagnetic transition at H c =26 T with a sharp step and saturates above H s =38 T, with 0.43 µ B /Np. On the other hand, the hard-axis magnetization for H ∥[001] increases linearly and saturates above H s =28 T, with 0.44 µ B /Np. These magnetization curves were discussed on the basis of reorientation and reduction of the magnetic moment.

Electrical and Magnetic Properties of R3Al11 (R = La, Ce, Pr, and Nd)

High-quality single crystals of R 3 Al 11 (R = La, Ce, Pr, and Nd) with the La 3 Al 11 -type orthorhombic crystal structure (space group I m m m ) have been grown by the Al-flux method. For Ce 3 Al 11 , signatures for ferromagnetic and antiferromagnetic orderings at T C = 6.3 K and T N = 3.2 K, respectively, have been observed in the magnetic susceptibility, magnetization, specific heat, and electrical resistivity. An antiferromagnet Pr 3 Al 11 , on the other hand, exhibits two magnetic transitions at T N1 = 12.6 K and T N2 = 3.1 K. An antiferromagnet Nd 3 Al 11 also exhibits multiple magnetic transitions at T N1 = 13.2 K, T N2 = 9.4 K, T N3 = 2.9 K, and T N4 = 1.77 K in zero magnetic field. The transition at T N4 has a first-order character. The crystalline electric field (CEF) analysis of magnetic susceptibility, magnetization and specific heat data shows that the CEF splitting is larger for Ce 3 Al 11 than for Pr 3 Al 11 and Nd 3 Al 11 . The CEF ground state of Pr 3 Al 11 is a singlet. Magnetic order o...