Anisotropic Magnetic Phase Diagram of PrB_6 Dominated by the O_<xy> Antiferro-Quadrupolar Interaction : Condensed Matter: Electronic Properties, etc.

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We have studied the specific heat, magnetoresistance and magnetization of PrB_6 which shows two successive phase ransitions at T_<IC> from the commensurate (C) to incommensurate (IC) magnetic phase and at TN from the IC to paramagnetic phase and obtained the magnetic phase diagram. The suppression of TN by the magnetic field shows the following anisotropy. Below ~12T, T^<<111>>_N < T^<<110>>_N < T^<<001>>_N and above ~12T, T^<<110>>_N < T^<<111>>_N < T^<<001>>_N. T_<IC> is suppressed by the magnetic field for H ‖<001> and <110> but T^<<111>>_N is enhanced largely with increasing magnetic field up to ~10T. It was found that the IC phase is divided into two phases below and above ~7T for the magnetic field around the H ‖ <111> direction. The anisotropy of T_N is explained by the different magnitude of the parallel and perpendicular magnetic susceptibility whose weights depend on the magnetic field direction. The anisotropic field dependence of T_<IC> at low magnetic field is explained by the different magnitude of the in-plane (H <110> and out-of-plane (H z) perpendicular magnetic susceptibility in the C phase which originates from the coexistence with the O_<xy > quadrupole order. The small ordered moment and twofold easy axis in the C phase are explained by the coexistence and competition between the O_<xy> quadrupolar and antiferromagnetic exchange interactions in the _5 triplet ground state.
社団法人日本物理学会の論文
2001-06-15