Magnetic ordering in clustered Fe-based materials synthesized from laser plasma (abstract)

Abstract

Using Mössbauer spectroscopy and the magneto-optical Kerr effect, we investigate how magnetic order arises and develops in Fe/C and Fe/Cr layered mixtures prepared by pulsed laser deposition. Two different magnetic transformations are found to occur in these systems under their thermal annealing. The first is the paramagnetic–ferromagnetic crossover that takes place at annealing temperatures of 420–570 K in dependence on the average iron content. Varying the latter quantity, we also observed the same crossover to the ferromagnetic state. The second transformation is magnetic hardening at 700–800 K. The specific feature of both transformations is that they occur within narrow ranges of annealing temperature (<10 K). The first transformation is supposed to result from an additional iron enrichment of Fe-rich clusters and is associated with magnetic phase transition near the Curie temperature. The cluster enrichment was directly observed with transmission electron microscopy and was also shown in small angle x-ray scattering patterns of the compositionally modulated structures. The observed sharpening of the magnetic behavior near the Curie temperature is presumably a manifestation of the clustered structure. The second transformation is found to be induced by the onset of crystallization and the formation of particles of the new Fe-rich phase.