Ultrafast signatures of magnetic inhomogeneity in Pd 1-x Fe x ( x  0.08) epitaxial thin

Roman.Yusupov@kpfu.ru Abstract. A series of Pd 1- x Fe x alloy epitaxial films ( x = 0, 0.038, 0.062, and 0.080), a material promising for superconducting spintronics, was prepared and studied with ultrafast optical and magnetooptical laser spectroscopies in a wide 4 – 300 K temperature range. It was found that the transition to the ferromagnetic state causes the qualitative modification of both the reflectivity and the magnetooptical Kerr effect transients. Nanoscale magnetic inhomogeneity of the ferromagnet/paramagnet type inherent in the palladium-rich Pd 1- x Fe x alloys reveals itself in an occurrence of a relatively slow, 10-25 ps, photoinduced demagnetization component following a subpicosecond one; the former vanishes at low temperatures only in the x = 0.080 sample. We argue that the 10-ps timescale demagnetization originates most probably from the d -electron diffusive transport in the conditions of the nanometer-scale magnetic inhomogeneity. The low-temperature amount of the residual paramagnetic phase can be deduced from the magnitude of the slow reflectivity relaxation component, and is estimated as ~ 30% for x = 0.038 and ~ 15% for x = 0.062 films. The minimal iron content ensuring the magnetic homogeneity of the ferromagnetic state in Pd 1- x Fe x alloy at low temperatures is about 7 