High Magnetic Field Behaviour of the Triangular Lattice Antiferromagnet, CuFeO₂

The high magnetic field behaviour of the triangular lattice antiferromagnet CuFeO_2 is studied using single crystal neutron diffraction measurements in a field of up to 14.5 T and also by magnetisation measurements in a field of up to 12 T. At low temperature, two well-defined first order magnetic phase transitions are found in this range of applied magnetic field (H // c): at H_c1=7.6(3)/7.1(3) T and H_c2=13.2(1)/12.7(1) T when ramping the field up/down. In a field above H_c2 the magnetic Bragg peaks show unusual history dependence. In zero field T_N1=14.2(1) K separates a high temperature paramagnetic and an intermediate incommensurate structure, while T_N2=11.1(3) K divides an incommensurate phase from the low-temperature 4-sublattice ground state. The ordering temperature T_N1 is found to be almost field independent, while T_N2 decreases noticeably in applied field. The magnetic phase diagram is discussed in terms of the interactions between an applied magnetic field and the highly frustrated magnetic structure of CuFeO_2