Soft x-ray magnetic circular dichroism study of magnetite nanoparticles

EXAFS and XANES analysis of oxides at the nanoscale

“…In principle, the study of the Fe L 2,3 -edge XAS spectra in Fe oxides may provide information about the oxidation state and, in some cases, allow one to separate the contributions of the magnetic moments of Fe ions in tetrahedral and octahedral sites (van Aken & Liebscher, 2002;van der Laan & Kirkman, 1992;Crocombette et al, 1995). More recently, Fe L 2,3 -edge XMCD has also been at the centre of many of the characterization studies of nominal magnetite NPs (Park et al, 2004;Goering et al, 2006;Huang et al, 2004;Yamasaki et al, 2009). However, the most common iron oxides exhibit similar Fe L 2,3 XAS and XMCD spectra because they are mainly governed by the point symmetry at the absorbing site (octahedral and tetrahedral in this case).…”

Orbital and spin moments of 5 to 11 nm Fe3O4 nanoparticles measured via x-ray magnetic circular dichroism

“…Our measured values for the orbital and spin components, reported in Table I, suggest a quenching of the orbital moment (M L $ 0) for all the three samples, both at 300 K and at 80 K. This orbital quenching agrees with theoretical calculations 17,18 and experimental observations in Fe 3 O 4 single crystal 8 as well as in other Fe 3 O 4 nanoparticles. 19,20 It appears that the quenching of the orbital moment remains unaffected by the nanostructuration. The values for the spin component M S and the resulting net magnetic moment M Fe are significantly higher than M L , but somewhat lower than the M Fe values reported elsewhere for bulk Fe 3 O 4 8,17,18 and other Fe 3 O 4 NPs.…”

“…To our knowledge, only a few XMCD studies have been performed on Fe 3 O 4 NPs. 19,20 Given the diversity of the NP shapes, sizes, and environments, results can vary significantly and there is still much to learn. Our results indicate that while the magnetic moment M Fe in the larger nanoparticles appears somewhat close to M Fe in Fe 3 O 4 single crystal, it may be reduced by a number of factors associated with the nanostructuration: the preparation method to fabricate the nanoparticles, which may lead to various degrees of purity of Fe 3 O 4 , with presence of maghemite, the particle environment, with a ligand shell that may alter the electronic properties at the surface, but also the particle shape and size, potentially leading to an increased fractional volume of an oxidized shell when the particles are reduced to a few nanometers in size.…”

Analysis of charge and orbital order in Fe3O4by FeL2,3Tanaka1, Chang2, Buchholz3 et al. 2013Phys. Rev. B8070View full textAdd to dashboardCite

“…The size of the ferromagnetic component of the orbital moments on B sites in magnetite has been debated and different values have been inferred from the measurements of the Fe L 2,3 x-ray absorption spectra with circularly polarized light. [61][62][63][64][65][66][67] However, the presence of the ferromagnetic component of the orbital moments on the B sites alone does not constitute strong evidence of the existence of the COO state, since the component can be merely induced by the ordered spins through the spin-orbit interaction as in many other magnetic compounds. It is, therefore, essential to detect the antiferromagnetic, i.e., noncollinear, component of the orbital moments more directly by measuring the size of the term Im[F zx ] of the RXD, which appears only with magnetic space group, using circularly polarized light with a magnetic applied field on the sample.…”