Femtosecond Optical and Magneto-Optical Spectroscopy Study of Magnetic and Electronic Inhomogeneities in a Pd0.94Fe0.06 Thin Film

The results of a femtosecond optical and magneto-optical spectroscopy study of a thin epitaxial film of a low-temperature magnetically soft Pd_0.94Fe_0.06 alloy on a ({dy001})-MgO substrate are reported. The photoinduced demagnetization and magnetization recovery times are determined. The latter increases critically at approaching the ferromagnetic ordering temperature T_C = 190 K from below. It is shown that the reflectivity dynamics after a photoexcitation pulse evolves from a two-exponential in the paramagnetic phase to a four-component at 80 K < T < T_C, simplifying to a three-component at T < 50 K. According to our interpretation, such an evolution, along with the manifestation of an additional increasing component in the magnetic response at 80 K < T < T_C, indicates a magnetic and electronic inhomogeneity of the film associated with the distribution of local iron concentrations. The fraction of small-scale inclusions of the paramagnetic phase is estimated as ≈10 vol %.