Structural Modification and Metamagnetic Anomaly in the Ordered State of CeOs2Al10

A caged compound CeOs2Al10, crystallizing in the orthorhombic YbFe2Al10-type structure, undergoes a mysterious phase transition at T_0=29 K. We report the results of electron diffraction, magnetization, and magnetoresistance for single crystals. Superlattice reflections characterized by a wave vector q = (0, -2/3, 2/3) observed at 15 K indicate a structural modification in the ordered state. Activation-type behavior of the electrical resistivity along the three principal axes below 50 K suggests gap opening in the conduction band. The magnetic susceptibility \chi = M/B is highly anisotropic, \chi_a>\chi_c>\chi_b, all of which sharply decrease on cooling below T_0. Furthermore, a metamagnetic anomaly in the magnetization and a step in the magnetoresistance occur at B=6-8 T only when the magnetic field is applied parallel to the orthorhombic c axis. However, T_0 hardly changes under magnetic fields up to 14 T, irrespective of the field direction. By using these data, we present a B-T phase diagram and discuss several scenarios for the mysterious transition.Comment: 6 pages, 7 figures, accepted for publication in Phys. Rev.

Ferromagnetic Transition in a Caged Compound NdOs2Zn20

AbstractMagnetic properties in a caged compound NdOs2Zn20 have been studied by the measurements of magnetization M, magnetic susceptibility M/B, and specific heat C. The measurements indicate that NdOs2Zn20 shows a structural transition at Ts = 62K and a ferromagnetic transition at TC = 0.6K. The structural transition is also observed in the La counter-part LaOs2Zn20 at Ts = 151K. The results of M (T)/B, M (B), and C(T) of NdOs2Zn20 are reproduced by a crystalline electrical field scheme with a Kramers doublet ground state

Anomalous Magnetic Phase Diagram of CeTe under High Pressure

We have investigated the anomalous ordered phase of CeTe under high pressure, which has been suggested to be an antiferroquadrupole ordered phase. An anisotropic magnetic phase diagram has been obtained from magnetization and specific heat measurements for the three main field directions along [100], [110], and [111]. We discuss the magnetic phase diagram using a two-sublattice mean-field calculation including antiferromagnetic and antiferroquadrupolar interactions. The anomalous ordered phase can be interpreted as an antiferromagnetic ordered phase, which is strongly affected by the antiferroquadrupolar interaction through the off-diagonal matrix element between the Γ7 crystal-field ground state and the Γ8 excited state.This work was supported by Grants-in-Aid for Scientific Research (Nos. 21204456, 21102515, and 2430087) from JSPS and MEXT

Heavy-fermion weak-ferromagnet YbRhSb

A new Yb-based compound YbRhSb with the orthorhombic -TiNiSi-type structure has been synthesized. The magnetic-susceptibility, magnetization, and specific-heat (Cp) measurements of single crystals revealed a ferromagnetic transition at TC = 2.7 K. An extrapolation of the Cp/T data below 1 K yields 370 mJ/mol K2 as the value, and the magnetic entropy reaches only 0.25R ln 2 at TC. The spontaneous moment is unusually small, 3×10–3µB/Yb for B||b, while the magnetization increases to 1.4µB/Yb when the field of 15 T is applied along the a axis. We ascribe the weak ferromagnetism to a canted antiferromagnetic structure based on the observation of a metamagnetic transition and the decrease of TC with the increase of magnetic field

Interplay between crystal electric field and magnetic exchange anisotropies in the heavy-fermion antiferromagnet YbRhSb under pressure

We report the pressure effect on the magnetic ground state of the heavy-fermion (HF) canted antiferromagnet YbRhSb (orthorhombic ɛ-TiNiSi-type) by means of magnetization and resistivity measurements using a single crystal. At ambient pressure, this compound undergoes a transition at TM1=2.7 K into a canted antiferromagnetic (AF) state with a small spontaneous moment of 3×10-3 μB/Yb. With increasing pressure P above 1 GPa, another magnetic transition occurs at TM2 above TM1, and TM1(P) has a deep minimum of 2.5 K at 1.7 GPa. For P≥2 GPa, the canted AF structure changes to a ferromagnetic (FM) one, where a large moment 0.4 μB/Yb lies in the orthorhombic b-c plane and a metamagnetic transition occurs at B || a = 1.5 T. This unusual FM state below TM3≅4.3 K is ascribed to the balance between the single-ion crystalline electric field (CEF) anisotropy with easy direction || a and the intersite exchange interaction with easy b-c plane. Furthermore, we have investigated the pressure dependence of TM3 up to 20.4 GPa using electrical resistivity measurements. The structural stability under pressures up to 19 GPa was examined by x-ray diffraction. We find that TM3 above 2.5 GPa steeply increases up to about 7 K, showing a broad maximum and then slightly decreases with increasing pressure above 8 GPa, while the structure remains unchanged. We attribute the enhancement of TM3 above 2.5 GPa to an increase of the CEF anisotropy with respect to magnetic exchange anisotropy. Finally, we compare and discuss the volume dependence of magnetic phase diagram of YbRhSb with the isostructural HF ferromagnet YbNiSn