In situsmall-angle x-ray and nuclear resonant scattering study of the evolution of structural and magnetic properties of an Fe thin film on MgO (001)

Abstract

Growth of magnetron sputtered Fe films on clean single crystalline MgO (001) substrate has been studied using in situ grazing incidence small angle x-ray scattering (GISAXS) and grazing incidence nuclear resonant scattering (GINRS) measurements. While GISAXS provides information about morphological changes, GINRS provides information about structural and magnetic properties, thus making it possible to correlate the evolution of magnetic properties with that of morphology and structure of the film. The film exhibits a Volmer-Weber type growth, with percolation transition occurring around 2 nm film thickness. Presence of a finite quadrupole splitting, as seen in GINRS measurements, suggests a significant distortion from cubic symmetry up to a film thickness of 3.5 nm, which can be attributed to hybridization between Fe 3d and O 2p orbitals at the interface as well as in-plane tensile strain induced as a result of coalescence of islands. Initially Fe islands exhibit superparamagnetic relaxation, while finite magnetic moment appears upon formation of macroscopic percolation islands. The film exhibits a weak perpendicular magnetic anisotropy (PMA), which vanishes concurrently with disappearance of structural distortion, suggesting that the observed PMA at least partly originates from inherent strain in the film. No presence of any known oxide of Fe was detected at the interface. More precise information about topological and magnetic structure of the interfaces between Fe and MgO layers is obtained using combined x-ray reflectivity and nuclear resonance reflectivity measurements on a 57 Fe/MgO multilayer. Measurements show that about two monolayers of Fe at the interface have a reduced hyperfine field, providing evidence for hybridization with O atoms, as predicted by theory.

In-situ growth of iron mononitride thin films studied using x-ray absorption spectroscopy and nuclear resonant scattering

“…It may be noted that when the thickness of the film is very small, typically below the percolation limit (about 2 nm for Fe), the film comprises of isolated grains and therefore the stress produced during the growth may lead to distortion in the cubic symmetry resulting in larger QS. Emergence of such QS was also observed in ultrathin Fe films during the in-situ growth of Fe films on MgO(001) [83] at 300 K. The gradual reduction in QS with increase in the thickness indicates that the system transforms towards cubic symmetry which is also evident from our N K-edge XANES measurements presented in section 3.3. More details about the influence of film thickness on such stress are discussed in section 3.4.…”

In situ soft x-ray absorption spectroscopic study of polycrystalline Fe/MgO interfaces

“…Thus, the additional thickness of 0.4 nm has not added to the intensity of prepeak, suggesting that 0.3 nm is the upper limit to the thickness of the interfacial oxide layer. earlier study on an identically prepared structure, it was found using nuclear forward scattering that an interfacial layer of ~0.4 nm thickness possesses an average hyperfine field of 30.8 T, as against 33 T for bcc iron metal [48,49]. This was taken as an evidence for hybridization of Fe with oxygen in the interfacial region.…”

Real-time tracking of the self-assembled growth of a 3D Ge quantum dot lattice in an alumina matrix

“…the long acquisition time which precludes an acceptable temporal resolution, compatibility with the deposition conditions etc.). Therefore, various strategies of real-time and in situ X-ray scattering experiments have been developed in the past (Vegso et al, 2012;Gibaud et al, 2004;Sharma et al, 2015;Renaud et al, 2009;Siffalovic et al, 2007;Hodas et al, 2017).…”