MAGNETIC-ORDERING IN FE-CONTAINING SPINODALLY DECOMPOSING MATERIALS SYNTHESIZED FROM LASER-PLASMA

Using Mossbauer spectroscopy and the magneto-optical Kerr effect, we investigate how magnetic order arises and develops at room temperature 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 paramagnetic-ferromagnetic crossover that takes place at annealing temperatures of 420 to 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 Fe-rich phase.