Field-induced magnetic phase transitions in a triangular lattice antiferromagnet CuFeO2 up to 14.5T

Neutron diffraction studies on a frustrated triangular lattice antiferromag net (TLA) CuFeO2 have been performed under an applied magnetic field up to 14.5 T. The first-field-induced state was found to be not the commensurate 5-sublattice (up arrow up arrow up arrow down arrow down arrow) magnetic st ate but rather an incommensurate complex helical state reflecting the Heise nberg spin character of orbital singlet Fe3+ magnetic ions. In contrast, th e second-field-induced state was found to be the 5-sublattice (up arrow up arrow up arrow down arrow down arrow) magnetic state predicted by the two-d imensional (2D) Ising spin TLA model with compeling exchange interactions u p to the 3rd neighbors.