José I. Arnaudas | Searcharxiv

arXiv2019

Magnetic ripple domain structure in FeGa/MgO thin films

The magnetic domain structure is studied in epitaxial Fe$_{100-x}$Ga$_x$/MgO(001) films with 0 $<$ x $<$ 30 and thicknesses below 60 nm by magnetic force microscopy. For low gallium content, domains with the magnetization lying in the film plane and domain walls separating micrometric areas are observed. Above x $\approx$ 20, the magnetic contrast shows a fine corrugation, ranging from 300 to 900 nm, suggesting a ripple substructure with a periodic oscillation of the magnetization. We discuss the presence of a random magnetic anisotropy contribution, that superimposed to the cubic coherent anisotropy, is able to break the uniform orientation of the magnetization. The origin of that random anisotropy is attributed to several factors: coexistence of crystal phases in the films, inhomogeneous distribution of both internal strain and Ga-Ga next nearest neighbor pairs and interface magnetic anisotropy due to the Fe-O bond.

cond-mat.mtrl-sci↗

arXiv2018

Crystal structure and local ordering in epitaxial Fe$_{100-x}$Ga$_x$/MgO(001) films

In this work we present a study of the structural properties of Fe$_{100-x}$ Ga$_x$ grown by Molecular Beam Epitaxy on Mg0(100). We combine long range and local/chemically selective X-ray probes (X-ray Diffraction and X-ray absorption spectroscopy) together with real space imaging by means of Transmission Electron Microscopy and surface sensitive $in situ$ Reflected High Energy Electron Diffraction. For substrate temperature $T_s$ below 400 $^o$C we obtain $bcc$ films while, for $x \approx$ 24 and $T_s \geq$ 400$^o$C the nucleation of the $fcc$ phase is observed. For both systems a Ga anticlustering or local range ordering phenomenon appears. The Ga/Fe composition in the first and second coordination shells of the $bcc$ films is different from that expected for a random Ga distribution and is close to a D0$_3$-like ordered phase, leading to a minimization of the number of Ga-Ga pairs. On the other side, a true long-range D0$_3$ phase is not observed indicating that atomic ordering only occurs at a local scale. Overall, the epitaxial growth procedure presented in this work, first, avoids the formation of a long range ordered D0$_3$ phase, which is known to be detrimental magnetostrictive properties, and second, demonstrates the possibility of growing $fcc$ films at temperatures much smaller than those required to obtain bulk $fcc$ samples.

cond-mat.mtrl-sci↗