Dynamics of first- and second-order phase transitions in amorphous magnetooptic TbFeCo films
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The dynamics of phase transformations in thin amorphous TbFeCo films under the action of ∼ 1 ps laser pulses is investigated. The films are heated to the Curie temperature in the amorphous state (T C1), to the crystallization temperature (T ac), and to the Curie temperature in the crystalline phase (T C2). The change in magnetization is detected by Faraday magnetooptic effect during and after the action of the heating pulse. A static external magnetic fieldH∼1−12 kOe, whose flux lines are directed perpendicular to the plane of the film, is used in the experiments. Amorphous TbFeCo films possess a perpendicular magnetic anisotropy, which on crystallization becomes reoriented in the plane of the film. It is observed that crystallization and magnetization reorientation occur during the heating pulse (within ∼ 1 ps). The spin subsystem is heated to the Curie temperature several picoseconds after the end of the laser pulse. The characteristic spin relaxation time is ∼ 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.
PACS numbers75.70.Ak 75.30.Kz 78.20.Ls
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