Structural and magnetic phase transitions of the 2D ferromagnetic fluoride TI2CuF4

A new transition phase has been observed in the copper complex fluoride, Tl2CuF4, with the K2NiF4-derived structure. A Rietveld refinement of the room-temperature X-ray powder pattern in the I4/mmm space group [a = 4.206(2) A; c = 13.673(5) A] has confirmed the antiferrodistortive arrangement of the eg orbitals of Cu2+. Around 200 K a structural phase transition to a low-temperature monoclinic phase has been evidenced by DSC and X-ray diffraction [space group I2/m, a = 4.182(2) A, b = 4.183(2) A, c = 13.492(6) A; β= 94.564(4)°]. Tl2CuF4 exhibits ferromagnetic properties below Tc = 10 K. The dependence of the magnetization on the applied field is characterized at 1.7 K by a coercive field of 2.5 × 10-2 T and a remanent magnetization of 0.6 μB. The phase sequence has been compared with those found in La2CuO4-type compounds. © 1996 Academic Press, Inc.