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

Using Mossbauer spectroscopy and the magneto-optical Kerr effect, we i nvestigate 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 s ystems under their thermal annealing. The first is paramagnetic-ferrom agnetic crossover that takes place at annealing temperatures of 420 to 570 K in dependence on the average iron content. Varying the latter q uantity, we also observed the same crossover to the ferromagnetic stat e. The second transformation is magnetic hardening at 700-800 K. The s pecific feature of both transformations is that they occur within narr ow ranges of annealing temperature (< 10 K). The first transformation is supposed to result from an additional iron enrichment of Fe-rich cl usters and is associated with magnetic phase transition near the Curie temperature. The cluster enrichment was directly observed with transm ission electron microscopy and was also shown in small angle x-ray sca ttering patterns of the compositionally modulated structures. The obse rved sharpening of the magnetic behavior near the Curie temperature is presumably a manifestation of the clustered structure. The second tra nsformation is found to be induced by the onset of crystallization and the formation of particles of the Fe-rich phase.