Determination of the magnetostrictive atomic environments in FeCoB alloys

Abstract

The atomic environments of Fe and Co involved in the magnetostriction effect in FeCoB alloys have been identified by differential extended x-ray fine structure (DiffEXAFS) spectroscopy. The study, done in amorphous and polycrystalline FeCoB films, demonstrates that the alloys are heterogeneous and that boron plays a crucial role in the origin of their magnetostrictive properties. The analysis of DiffEXAFS in the polycrystalline and amorphous alloys indicates that boron activates magnetostriction when entering as an impurity into octahedral interstitial sites of the Fe bcc lattice, causing its tetragonal distortion. Magnetostriction would be explained then by the relative change in volume when the tetragonal axis of the site is reoriented under an externally applied magnetic field. The experiment demonstrates the extreme sensitivity of DiffEXAFS to characterize magnetostrictive environments that are undetectable in their related EXAFS spectra.

Development of FeCoB/Graphene Oxide based microwave absorbing materials for X-Band region

“…The pattern of the plots typically indicates the formation of combined polycrystalline amorphous particles. As reported by Diaz et al [10], the XRD pattern indicates the formation of (Fe 80 Co 20 ) 90 B 10 .…”

“…E5071C) within X-Band frequency range (8)(9)(10)(11)(12). If any microwave absorbing composite materials contains both dielectric and magnetic particles [13][14][15][16][17], then according to Nicolson-Ross model, the input impedance (Z in ), scattering parameter (S 11 ) and …”

Atomic-scale mechanisms for magnetostriction in CoFe2O4 and La0.5Subı́as1, Cuartero2, García3 et al. 2019Phys. Rev. BSelf Cite9030View full textAdd to dashboardCite

“…Since the dependence of the change in 𝑠𝑠 𝑗𝑗 with the magnetic field is not known, we can either directly compare the local magnetostriction strains determined by the DiffEXAFS analysis with the macroscopic magnetostriction values measured in the polycrystalline samples or, following the approach used by J. Díaz et al in Ref. [18], we can associate a specific j th coordination shell in EXAFS with a specific crystal direction. Then, we can define a magnetostriction coefficient λ 𝐷𝐷𝑗𝑗 measured by DiffEXAFS as…”

“…However, its sensitivity to determine local distortions is far from the expected one to be able to measure the strain coming from MS though it can be improved by the subtraction of XAS spectra. In fact, DiffXAS [15,16] has demonstrated sensitivity to the atomic displacements of the order of femtometers and it has made the direct assessment of local-scale MS possible, as reported for several metal alloys [17,18].…”

“…We have also performed an empirical analysis of the DiffEXAFS data using experimental backscattering ( ) and ( ) for the isolated first and second coordination singleshells retrieved by Fourier filtering its related EXAFS spectra. Both methods of analysis gave consistent results so we only present the results from the first more accurate analysis.Since the dependence of the change in with the magnetic field is not known, we can either directly compare the local magnetostriction strains determined by the DiffEXAFS analysis with the macroscopic magnetostriction values measured in the polycrystalline samples or, following the approach used by J. Díaz et al in Ref [18],. we can associate a specific j th coordination shell in EXAFS with a specific crystal direction.…”