Femtosecond optical and magneto-optical spectroscopy study of magnetic and electronic inhomogeneities in a Pd$_{0.94}$Fe$_{0.06}$ 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$_{0.94}$Fe$_{0.06}$ 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 $T_{\mathrm{C}}=190$ 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 $< T < T_{\mathrm{C}}$, 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 $< T < T_{\mathrm{C}}$, 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 $\approx 10$ vol %.