High-magnetic-field behavior of the triangular-lattice antiferromagnet CuFeO2

The high-magnetic-field behavior of the triangular-lattice antiferromagnet CuFeO2 is studied using single crystal neutron diffraction measurements in a field of up to 14.5 T and also by magnetization 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 parallel to 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 four-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 CuFeO2