High-pressure studies of antiferromagnetic oxides with a delafossite-type triangular structure

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Since the high-Tc superconductor was discovered, great attension has been paid to low-dimensional transition metal oxides, from the view of strongly correlated electron systems. Some oxides with a delafossite-type structure have been attractive because of its low-dimensional triangular structure. CuFeO_2 has magnetic Fe^<3+> layers, which form a layered triangular lattice frustrated antiferromagnet, separated by nonmagnetic Cu^+ and O^<2-> layers. In a frustrated system, the magnetic phase transitions take place under a subtle balance of magnetic interactions. CuFeO_2 exhibits two successive antiferromagnetic transitions at 13 K(T_<N1>) and 9 K (T_<N2>). Another antiferromagnetic oxides, CuCrO_2 and transparent semiconductor, CuAlO_2 have also been investigated. Since impurity largely affects the antiferromagnetism of CuFeO_2, the pressure effect is expected to affect the magnetic state. In this study we have carried out magnetic susceptibility measurements on the antiferromagnetic tra … More nsition temperature of CuFeO_2 under high pressure and electrical resistivity measurements on CuCrO_2 and CuAlO_2 under high pressure. From the magnetic susceptibility measurements of CuFeO_2, the T_<N1> and T_<N2> decrease with pressure up to 0.7 GPa at a rate of -1K/GPa. If the T_<N1> and T_<N2> decrease linearly at a rate of -1 K/GPa, it disappears at 10 GPa. Then it is very interesting to perform high-pressure studies at more than 10 GPa, since a new magnetic phase can be expected at the pressure where the magnetic ordering state disappears, as observed in UGe_2. From the preliminary electrical resistivity measurements under high pressure, the resistivity decreases to 0.1 times value at 10 GPa. The susceptibility and electrical resisitivity measurements are in progress at_higher pressures. In the electrical resistivity measurements of CuCrO_2 and CuAlO_2 under high pressure, the resistivity decreases a little with increasing pressure. The resistivity measurements under much higher pressure are in progress. Less