Magnetic phase diagram of the nearly 2D Heisenberg ferromagnet (CH3NH3)2CuCl4 in a transverse magnetic field

The magnetic phase diagram of the nearly 2D ferromagnet (CH3NH3)(2)CuCl4 (T-C = 8.85 K) in magnetic fields applied perpendicular to the easy axis is obtained. In this system, the ferromagnetic moments lie in planes (ab planes) formed by the Cu atoms and point along the a crystallographic direction. For field applied along b-axis (intermediate anisotropy axis), a second-order transition to the paramagnetic phase occurs at the field of 80 Oe at the lowest measured temperature (T = 1.8 K). When the field is applied in a direction perpendicular to the Cu planes (c-axis) the paramagnetic phase is reached only above 1500 Oe after a double transition. The first transition (similar to 500 Oe) is suggested to be an order-order transition in which a spin reorientation occurs. The obtained in-plane and out-of-plane anisotropy are H-A(in) = 80 and H-A(out) = 1500 Oe, respectively. (C) 2003 Elsevier Science B.V. All rights reserved.