Orbital magnetic moment and coercivity ofSiO2-coated FePt nanoparticles studied by x-ray magnetic circular dichroism

Abstract

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 (M orb ) to the spin magnetic moment (Mspin) of Fe to be M orb /Mspin = 0.08. This M orb /Mspin 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 non-interacting single-domain nanoparticles with the Hc distributed from 1 T to 5 T.

Characterization techniques for nanoparticles: comparison and complementarity upon studying nanoparticle properties

“…In XMCD, one can eliminate the extrinsic magnetic signals, such as those from oxidized Fe and those from the diamagnetic SiO 2 coating. 325 FeRh NPs were also studied with XMCD, by Chaudret et al XMCD constitutes a valuable tool to unravel the role of each element in the overall magnetic behaviour of bimetallic NPs. Powerful sum rules permit the direct identification from the experimental spectra not only the value of spin and orbital contributions to the total magnetic moment, but also its orientation.…”

Origin of High Activity and Durability of Confined Ordered Intermetallic PtCo Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Fuel Cell Operating Conditions

“…Surface modifications, such as metal oxide or carbon shell coatings, have been reported as an effective method for preventing particle agglomeration, − while the dense surface coating can also hinder the diffusion of the reactant and reduce the exposed active sites, ultimately leading to decreased MA. , The nitrogen-doped carbon coating shells (CN x ) have been identified as efficient protecting coatings to stabilize the nanoparticle against particle agglomeration under fuel cell operation conditions and improve resistance to the sintering in the thermal treatment. ,, N in the carbon shells not only introduces defects that benefit the reactant diffusion but also boosts the catalyst activity by offering additional charge polarization . Thus, it has been applied particularly in synthesizing small-sized intermetallic alloy nanoparticle catalysts .…”

Electronic and magnetic properties of off-stoichiometric Co2MnβSi/MgO interfaces studied by x-ray magnetic circular dichroism

“…By applying the sum rules [1,2,20,[25][26][27][28][29][30][31], we obtained the spin and orbital magnetic moments of the Mn atom from the XAS and XMCD spectra. We assumed the contribution of the dipole operator term T z in the spin sum rule to be negligibly small because the Mn atom in CMS is located at the high-symmetry T d site [2].…”

“…To determine the Co magnetic moment, we applied the sum rules [1,2,20,[25][26][27][28][29][30][31] as in the case of the Mn L 3,2 -edges. Since the Co atoms are also in the highlysymmetry T d crystal field, we again neglect the T z term in the spin sum rule [2].…”

“…FIG.2:(Color online) Mn composition (β) dependence of the Mn spin magnetic moment deduced from the XMCD data using the sum rules[1,2,20,[25][26][27][28][29][30][31] compared with that given by the present KKR-CPA calculation. The magnetic moments of Mn in CMG by Singh et al[20] are shown by dotted lines.…”