Composition-dependent ratio of orbital-to-spin magnetic moment in structurally disorderedFexPt1−xnanoparticles

The ratio of orbital-to-spin magnetic moment μ e f f L/μ e f f S averaged over the element-specific contributions of Fe and Pt has been measured for 3-nm Fe x Pt 1 - x nanoparticles at room temperature using the multifrequency electron paramagnetic resonance method for different concentrations of Fe. From a detailed g-factor analysis we determine that the ratio decreases from μ e f f L/μ e f f S=0.049 for x=0.43 to μ e f f L/μ e f f S=0.016 for x=0.70 which is much smaller than the bulk iron value (μ F e L/μ F e S=0.045). The observed concentration dependence is much stronger than the one calculated for Fe x Pt 1 - x bulk samples and reveals likely changes of the confined electronic structure of the nanoparticle system. The ratio μ e f f L/μ e f f S takes the lowest value at the concentration (x =0.70) where the magnetic anisotropy energy vanishes in bulk alloys. For x>0.72 a phase transition from a fcc to the Fe bcc structure occurs resulting in the increased bulk ratio again.