The comparison of magnetic properties of nanocrystalline Fe-M-Cu-Nb-Si-B (M = Co, Ni) thin films and ribbons

An attempt is made to study the structure and the magnetic properties of the films of Fe-M-Cu-Nb-Si-B (M = Co. Ni) alloys. Thin films have been prepared by ion beam sputtering. The structural observations showed the process of thin film crystallization after annealing. The differences of magnetic domain structure depending upon the heat treatment were observed. The influence of annealing temperature on the coercivity was examined. The minimum of the coercivity was shifted from one annealing temperature of 550°C for ribbons to temperature range 350°C-420°C for thin films and the minimal value of the coercivity of thin films is about 50 times higher than that one for ribbons

Structural and magnetic properties of cobalt iron disulfide (CoxFe1−xS2) nanocrystals

Abstract We report on synthesis and investigation of nanocrystalline cobalt-iron-pyrites with an emphasis on nanocrystal structure, morphology and magnetic behavior. The nanocrystals (NCs) were 5–25 nm in diameter as characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). With an increase in Fe fraction, X-ray diffraction and small-angle-X-ray scattering (SAXS) showed a systematic decrease in lattice constant, primary grain/NC size (15 to 7 nm), and nanoparticle (NP) size (70 to 20 nm), respectively. The temperature dependence of the DC magnetization and AC susceptibility versus frequency revealed a number of magnetic phases in Co x Fe1−x S2. Samples with x = 1 and x = 0.875–0.625 showed evidence of superspin glass (SSG) behavior with embedded ferromagnetic (FM) clusters of NPs. For x = 0.5, samples retained their mixed phases, but showed superparamagnetic (SPM) behavior with antiferromagnetic clusters suppressing magnetic dipolar interactions. Below x = 0.5, the pyrites show increasing paramagnetic character. We construct a phase diagram, which can be understood in terms of competition between the various dipolar, exchange, inter- and intracluster interactions. Our results suggest that NC size and shape can be tuned to engineer spin-polarized ferromagnetism of n-doped iron pyrite