The role of surface to bulk ratio on the development of magnetic anisotropy in high Ga content Fe100-xGax thin films

Abstract

In this work we show the development of bulk in-plane magnetic anisotropy in high Gacontent (Ga = 28 at. %) Fe 100-x Ga x thin films as the layer thickness increases. This result is in clear contrast with the generally reported decrease of this anisotropy with the film thickness. We propose the interrelation between the enhancement of the Ga-pair correlations and a collinear distortion of the bcc structure within the sample plane as the origin of the magnetic anisotropy. Our results have been obtained by employing a combination of long and local range structural probe techniques with bulk and surface magnetic characterization techniques. The key point shown in this work is that the inplane structural anisotropy and hence, the magnetic anisotropy, are developed as the layer thickness increases. This fact strongly suggests that the surface to bulk free energy ratio plays a key role in the formation of ordered phases with a distorted bcc cell in Fe 100-x Ga x films with x around 28 at. %. Our work also shows the arising of new phenomena in these high Ga content alloys due to the close correlation between structural and magnetic properties.

Local and Medium Range Order Influence on the Magnetic Behavior of Sputtered Ga-Rich FeGa Thin Films

“…Recently, the correlation between microstructure and the development of an inplane magnetic anisotropy in Ga-rich FeGa alloys around the second peak has been reported. [19][20] In particular, the local range order promoted by the use of different sputtering regimes, ballistic or diffusive, was reported in a previous work. 19 To study the local range order, the use of X-ray absorption fine structure (XAFS) measurements are crucial since they can provide information about the electronic structure and local geometry of the scattering atom when using x-ray absorption near edge structure (XANES), and about the degree of disorder by means of extended x-ray absorption fine structure (EXAFS).…”

“…Similar XANES results can be found in works about Ga-rich FeGa thin films. [19][20] The shape and intensity of the white line is related to the proportion of the different structural phases that can be present in these samples that are: A2, B2, and D0 3 . In order to highlight the differences, we present in figure 3.c, the subtracted spectra with respect to the layer deposited at the lowest growth power.…”

“…The thickness of the layers has been chosen in order to promote the existence of a clear inplane magnetic anisotropy. 20 We have used an Ar pressure of 0. The XAFS measurements were performed at BM25-Spline in the ESRF, the European Synchrotron in Grenoble (France).…”

“…[2][3][4][5][6][7][8][9][10][11][12][13][14] Less has been reported on Fe 100-x Ga x alloys with compositions around the second maxima, in spite of their intrinsic interest. 1,[15][16][17][18][19][20] The metastable diagram phase predicts an A2 single phase state just for Ga contents up to 21 at. %.…”

“…19 To study the local range order, the use of X-ray absorption fine structure (XAFS) measurements are crucial since they can provide information about the electronic structure and local geometry of the scattering atom when using x-ray absorption near edge structure (XANES), and about the degree of disorder by means of extended x-ray absorption fine structure (EXAFS). 9,[19][20][21][22] In the sputtering process, neutrals (atoms ejected from the target upon the impact of energetic particles) suffer collisions on their movement from the target to the substrate. [23][24][25] If the number of collisions is low, neutrals keep their momentum and energy till the substrate, and the sputtering growth takes place under ballistic flow.…”