We have investigated the spin and orbital magnetic moments of Fe in FePt nanoparticles in the L10-ordered phase coated with SiO2 by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at the Fe L2,3 absorption edges. Using XMCD sum rules, we evaluated the ratio of the orbital magnetic moment (Morb) to the effective spin magnetic moment (Mspineff) of Fe to be Morb/Mspineff=0.08. This Morb/Mspineff value is comparable to the value (0.09) obtained for FePt nanoparticles prepared by gas phase condensation, and is larger than the values (∼0.05) obtained for FePt thin films, indicating a high degree of L10 order. The hysteretic behavior of the FePt component of the magnetization was measured by XMCD. The magnetic coercivity (Hc) was found to be as large as 1.8 T at room temperature, ∼3 times larger than the thin film value and ∼50 times larger than that of the gas phase condensed nanoparticles. The hysteresis curve is well explained by the Stoner-Wohlfarth model for noninteracting single-domain nanoparticles with the Hc distributed from 1 to 5 T.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 25 Jul 2014|