THE SPIN REORIENTATION TRANSITION IN ERBIUM IRON-GARNET - A NEUTRON AND X-RAY TOPOGRAPHICAL STUDY

The spin reorientation transition between the rhombohedral (T > 79 K) and tetragonal (T < 73 K) magnetic phases of erbium iron garnet is studied by neutron- and X-ray topography. Both the hysteresis in temperature of the nearly magnetic 220 reflection, and the visualisation of the phase coexistence in the range 73-79 K, indicate a first-order transition. Its detailed behaviour in thick (1 mm) crystals appears to be extremely dependent on the magnetic and thermal sample history, as well as on mechanical constraints, which might explain partly contradictory reports concerning the order and the exact temperature of the spin reorientation phase transition. Reproducible results were obtained on a thin (0.1 mm) ErIG (112) platelet.