Edge X-ray Magnetic Circular Dichroism Research Articles

Influence of magnetocrystalline anisotropy on rare-earthL2,3-edge x-ray magnetic circular dichroism spectra

We present an x-ray magnetic circular dichroism (XMCD) study performed at the Sm and Er ${L}_{2,3}$-edges for the ${R}_{2}{\mathrm{Fe}}_{17}$ compounds $(R=\mathrm{rare}$ earth) and their ${R}_{2}{\mathrm{Fe}}_{17}{\mathrm{H}}_{x}$ and ${R}_{2}{\mathrm{Fe}}_{17}{\mathrm{N}}_{x}$ derivatives. The modification of the magnetocrystalline anisotropy by interstitial nitrogen atoms affects the shape of the XMCD signals recorded at both Sm and Er ${L}_{3}$ edge. On the other hand, while the change from planar to uniaxial anisotropy does not modify the Sm ${L}_{2}$-edge XMCD signal, the sign of the Er ${L}_{2}$-edge XMCD spectrum is reversed. These results are discussed in terms of the effect of the magnetocrystalline anisotropy on the XMCD spectra at rare-earth ${L}_{2,3}$ absorption edges of R-Fe intermetallic systems.

NMR and X-MCD study of Sr 1−3 xBa 1+ xLa 2 xFeMoO 6

A study of La influence on molybdenum and iron magnetic states in the Sr 1−3 x Ba 1+ x La 2 x FeMoO 6 series ( x=0, 0.1, 0.2, 0.3) is reported. The main line and a low frequency satellite of the Mo NMR spectra are attributed to ideal and defect sites. The structure of the main line with increasing La content indicates a local effect of electron doping on Mo sites. Fe:K edge X-ray magnetic circular dichroism spectra show an increased polarisation of the Fe 4p states with La doping. The Fe:K absorption edges show an unchanged Fe ionic state but an increased localisation of the Fe electronic states.

Pressure-Induced Magnetic Transition in Fe4N Probed by FeK-edge XMCD Measurement

X-ray magnetic circular dichroism (XMCD) of γ'-iron nitride (Fe 4 N) was recorded at Fe K -edge under high pressue up to 27 GPa. The XMCD intensity decreased remarkably with pressure, and vanished at 24 GPa. Compressibility was measured by the X-ray diffraction method. These results indicate that Fe 4 N undergoes a second-order phase transition from the ferromagnetic state to a paramagnetic state without any structural change. The pressure-induced demagnetizing process is discussed in terms of the Fe magnetic states in the local environment.

Local environment surrounding ferromagnetically ordered Mn in Mn/GaAs digital alloys and (Mn, Ga)As random alloys

The local environment surrounding ferromagnetically ordered Mn in Mn/GaAs digital layers and (Ga, Mn)As random alloys has been selectively probed using a combination of local structural information obtained by x-ray magnetic circular dichroism (XMCD) and extended x-ray absorption fine structure (EXAFS) techniques. The Mn/GaAs digital layers and (Ga, Mn)As random alloys exhibit an exceptionally large XMCD of $42%\ifmmode\pm\else\textpm\fi{}2%$ and $39%\ifmmode\pm\else\textpm\fi{}2%$ at the Mn ${L}_{3}$ absorption edge, indicating that a high percentage of at least 71% and 66% Mn atoms with robust local magnetic moments actually participate in the ferromagnetic ordering, respectively. The observed Mn ${L}_{3}$-edge XMCD spectra and Mn K-edge EXAFS spectra are very similar for the Mn/GaAs digital layers and (Ga, Mn)As random alloys, but clearly different from those found in a reference MnAs film. These results provide direct evidence that the ferromagnetism observed in the Mn/GaAs digital layers and (Ga, Mn)As random alloys is mainly due to the Mn atoms occupying the Ga sites in the GaAs host instead of possible MnAs magnetic clusters.

X-ray magnetic circular dichroism study of spin reorientation transitions of magnetic thin films induced by surface chemisorption

Spin reorientation transitions of Co and Ni thin films induced by surface chemisorption have been investigated for CO-adsorbed Co/Pd(111) and CO- and H-adsorbed Ni/Cu(001) by means of Co ${L}_{\mathrm{I}\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}}$- and Ni ${L}_{\mathrm{I}\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}}$-edge x-ray magnetic circular dichroism (XMCD). For four to six monolayer (ML) Co/Pd(111), a spin reorientation transition from surface parallel to perpendicular magnetization has been observed at 200 K after CO dosage. The region of perpendicular magnetic anisotropy (PMA) becomes about 3 ML thicker at this temperature. For Ni/Cu(001), similar transitions have been confirmed when the layers are covered with CO or H, and the PMA range is also expanded, in this case by about 2 ML. The observed stabilization of perpendicular magnetic anisotropy due to chemisorption is ascribed to quenching of the surface parallel magnetic orbital moment. The effects of the fashion in which adsorption occurs on the easy axis of thin-film magnetization are also examined by comparing the differences in behavior between CO- and H-adsorbed Ni films.

Multiple scattering approach to Co K-edge XMCD and XANES spectra in Gd–Co alloys

We have measured and analyzed Co K-edge X-ray absorption near edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) near edge spectra in crystalline and amorphous GdCo 2 alloys. We have used a semi-relativistic full multiple scattering approach to the analyses of the XMCD spectra. A general formula is obtained which is applicable to randomly oriented systems in space. Useful information is obtained on both the electronic and geometric structure around a Co atom. The difference in XANES and XMCD spectra between crystalline and amorphous GdCo 2 is well explained by models referring to the anomalous X-ray scattering result, where three Gd atoms in the second shell are removed away. The calculated XANES are not so sensitive to the electronic structure, whereas the calculated XMCD spectra are rather sensitive to the spin polarization on Co atoms. The result shows that the spin polarization on Co atoms in GdCo 2 alloys is smaller than that in Co metals.

Magnetic Interaction between Adsorbed NO andfccCo(001) Thin Films Studied by X-ray Magnetic Circular Dichroism

N K -, O K - and Co L III,II -edge X-ray magnetic circular dichroism (XMCD) was investigated for NO adsorbed on ultrathin fcc -Co(001) films which show both in-planar and perpendicular magnetic anisotropies. Large suppression of spin and orbital magnetic moments of Co was observed upon NO adsorption. Both N and O K -edge XMCD spectra show negative signs at the NO 2π * resonance, irrespective of in-plane and perpendicular magnetic anisotropies. This finding implies the parallel alignment of the NO 2π * orbital magnetic moments with the total magnetization. The results are comparatively discussed with the previous works on CO on Co and Ni films and are interpreted by a simple chemical bonding scheme.

XMCD measurements and calculations at the Co K edge in YCo 4B

The effects of B for Co substitution in RCo 5 compounds on the Co K edge X-ray magnetic circular dichroism (XMCD) signal is studied. Calculations of the YCo 4B XMCD spectrum have been performed. These calculations were based on band structure calculations and multiple scattering theory of XMCD. A good agreement is found between the calculations and the experiment.

OK-edge x-ray magnetic circular dichroism of atomic O adsorbed on an ultrathin Co/Cu(100) film: Comparison with molecular CO on Co/Cu(100)

We observed O K-edge x-ray magnetic circular dichroism (XMCD) of atomic O adsorbed on a fcc Co thin film grown epitaxially on Cu(100). The XMCD of $c(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{O}$ showed a negative sign at the $\mathrm{O}1\stackrel{\ensuremath{\rightarrow}}{s}2p$ transition. The negative sign indicates parallel alignment of the O orbital moment with the substrate magnetization. This finding is in contrast to the CO/Co/Cu(100) case where a positive XMCD was observed at the $\mathrm{O}1\stackrel{\ensuremath{\rightarrow}}{s}\mathrm{CO}2\ensuremath{\pi}*$ transition. A possible explanation for this discrepancy is proposed referring to recent theoretical prediction [Pick et al., Phys. Rev. B 59, 4195 (1999)].

Co magnetic instability study in RCo 3 by XMCD

We have performed a temperature-dependent study of the Er L 3 and Co K edge X-ray magnetic circular dichroism (XMCD) in a (Er, Y)Co 3 system. The Co K XMCD signal shows a clear change at 35 K, which has been associated to a Co metamagnetic transition, previously reported. However, around the compensation temperature T com, no discontinuity is observed, as should be expected if the magnetic moments were just reversed. The observed smooth passage through T com is interpreted as a transition from a collinear to a non-collinear Co ordering, where Co moments assume intermediate orientations. The analysis of the E2/E1 ratio has allowed us to gain some insight into the magnetic properties of the 5d band. Finally, from our XMCD measurements, it is possible to complete the magnetic phase diagram of (Er, Y)Co 3, previously proposed.

Fe K-edge x-ray magnetic circular dichroism study in R6Fe23 (R=Ho and Y) compounds near compensation temperature

We present a x-ray magnetic circular dichroism (XMCD) study performed at the Fe K edge in R6Fe23 compounds exhibiting magnetic compensation (R=Ho and Y). The Fe K-edge XMCD signal has been identified as due to both Fe itself and rare-earth contributions. Following a simple two-sublattices model for the analysis of the dichroic signal the contribution of the rare-earth sublattice to total Fe K-edge XMCD signal has been extracted and proven to be directly correlated to the R magnetic moment.

X-ray magnetic circular dichroism on Co monodispersive cluster assemblies

X-ray absorption near edge structure (XANES) spectra and x-ray magnetic circular dichroism (XMCD) spectra at the Co K edge have been measured for Co clusters with the mean diameter d = 6-13 nm. The spectral analysis indicates that the fcc phase is predominant for d = 6 nm, while the hcp phase gradually increases with increasing d in agreement with the results of transmission electron microscopy. The 4p orbital moments of clusters tend to decrease in the smaller cluster, but the reduction is small compared with the case of the multilayers, suggesting the importance of surface effects of the Co cluster system.

X-ray Magnetic Circular Dichroism Sum Rule Analysis of the Blue Copper Site in Plastocyanin. A Probe of Orbital and Spin Angular Momentum

Cu L edge X-ray magnetic circular dichroism (XMCD) spectroscopy has been used to study the electronic structure of the blue copper site in plastocyanin. Application of the orbital angular momentum sum rule leads to an experimental (Cu 3d specific) orbital moment 〈Lz〉 of 0.07 ± 0.02 ℏ/Cu atom. This compares to 0.054 ℏ derived from the EPR measurements and 0.059 ℏ/Cu atom from a SCF-Xα-SW calculation. Application of the spin angular momentum sum rule leads to an experimental spin moment 〈Sz〉 of 0.18 ± 0.02 ℏ/Cu atom, compared to 0.21 ℏ/Cu atom by SCF-Xα-SW. XMCD sum rule analysis should be a useful probe of electronic structure for many other problems in inorganic and bioinorganic chemistry.

Modification of the rare-earth magnetic moment upon hydrogen absorption inR−Feintermetallics probed by FeK-edge x-ray magnetic circular dichroism

We present a systematic x-ray magnetic circular dichroism (XMCD) study performed at the Fe $K$ edge on the hydride derivatives of several $R\ensuremath{-}\mathrm{Fe}$ intermetallic materials ($R$=rare earth and Y). The XMCD signal is identified as being rare-earth dependent. The analysis of the dichroic signal has been performed according with a two-sublattice model making a parallel to standard magnetization procedure. The contribution of the rare-earth sublattice to the total Fe $K$-edge XMCD signal has been extracted and proven to be directly correlated to the $R$ magnetic moment, which is determined to decrease upon hydrogen absorption.

X-ray magnetic-circular-dichroism probe of a noncollinear magnetic arrangement below the spin reorientation transition inNd2Fe14B

The experimental detection of a spin reorientation phase transition by means of Fe $K$-edge x-ray magnetic circular dichroism (XMCD) is reported for ${\mathrm{Nd}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$. The temperature dependence of the XMCD signals at both Fe ($K$ edge) and Nd (${L}_{2,3}$ edges) is compared to that of the mutual orientation of the Fe and Nd magnetic moments derived from macroscopic magnetic measurements. The present study results in the experimental probe of the existence of a noncollinear arrangement of both Fe and Nd magnetic moments, throughout the spin reorientation transition.

K edge X-ray magnetic circular dichroism in molecule-based magnets

We report X-ray magnetic circular dichroism at the K edge of Cr, Mn, Ni and N, in molecule-based magnets of the Prussian Blue family. The effect (0.5 %) is visible at the metallic K edge in the white line. An interpretation of the XMCD structure is proposed and a multiplet calculation at the nickel edge reported.