Role of Magnetostrictive Effect in Magnetization Dynamics of SmFe Thin Films

Laser induced magnetization dynamic behaviors of SmxFe1–x thin films with tunable x (0.25 ≤ x ≤ 0.5) are investigated by the time-resolved magneto-optical Kerr effect. It is found that the demagnetization process is accomplished by a two-stage process, the demagnetization time of stage I is within 1.0 ps (t1) for all the samples with different x, while it increases from 0 to 16 ps at stage II (t2) due to the reduced exchange coupling. By introducing an additional magneto-elastic energy contribution, the dispersion relation of precession frequency is deduced, by which the field-dependent frequency curves are well fitted.