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

Abstract The magnetic phase diagram of the nearly 2D ferromagnet (CH 3 NH 3 ) 2 CuCl 4 ( 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 (∼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.