DYNAMICS OF FIRST-ORDER AND 2ND-ORDER PHASE-TRANSITIONS IN AMORPHOUS MAGNETOOPTIC TBFECO FILMS

The dynamics of phase transformations in thin amorphous TbFeCo films u nder the action of similar to 1 ps laser pulses is investigated. The f ilms are heated to the Curie temperature in the amorphous state (T-C1) , to the crystallization temperature (T-ac), and to the Curie temperat ure in the crystalline phase (T-C2) The change in magnetization is det ected by Faraday magnetooptic effect during and after the action of th e heating pulse. A static external magnetic field H similar to 1-12 kO e, whose flux lines are directed perpendicular to the plane of the fil m, is used in the experiments. Amorphous TbFeCo films possess a perpen dicular magnetic anisotropy, which on crystallization becomes reorient ed in the plane of the film. It is observed that crystallization and m agnetization reorientation occur during the heating pulse (within simi lar to 1 ps). The spin subsystem is heated to the Curie temperature se veral picoseconds after the end of the laser pulse. The characteristic spin relaxation time is similar to 10 ps. A model of the dynamics of the electronic, spin, and phonon subsystems that makes it possible to explain the experimental results is proposed on the basis of the data obtained. (C) 1998 American Institute of Physics. [S0021-3640(98)01311 -5].