Magnetic phase diagram of the low-anisotropy antiferromagnet Cs2FeCl5·H2O

From magnetization and ac susceptibility measurements we obtain the complete magnetic phase diagram of single crystals of Cs2FeCl5·H2O for magnetic field up to 15 T. The magnetic field was applied along the directions parallel and perpendicular to the easy axis and the magnetization measured to temperatures down to 0.5 K. At zero magnetic field the antiferromagnetic ordering occurs at TN=6.63 K. For the field applied parallel to the easy axis the antiferromagnetic (AF) to the spin-flop (SF) transition occurs for fields from 1.4 T to 1.1 T depending on the temperature. The low temperature transition from the (SF) to the paramagnetic (P) phase occurs at 13.15 T. In the perpendicular configuration this transition occurs at fields around 13.5 T. From the extrapolation of the transition fields to zero temperature, we obtain a ratio of the anisotropy field HA to exchange field HE, α=HA/HE=(1.4±0.2)×10−2. A comparison with the phase diagram measured for MnF2 is included.