Influence of the sputtering flow regime on the structural properties and magnetic behavior of Fe-Ga thin films (Ga ∼ 30 at.%)

Abstract

In this paper we analyze the structure of Fe-Ga layers with a Ga content of ∼30 at.% deposited by the sputtering technique under two different regimes. We also studied the correlation between the structure and magnetic behavior of the samples. Keeping the Ar pressure fixed, we modified the flow regime from ballistic to diffusive by increasing the distance between the target and the substrate. X-ray diffraction measurements have shown a lower structural quality when growing in the diffusive flow. We investigated the impact of the growth regime by means of x-ray absorption fine structure (XAFS) measurements and obtained signs of its influence on the local atomic order. Full multiple scattering and finite difference calculations based on XAFS measurements point to a more relevant presence of a disordered A2 phase and of orthorhombic Ga clusters on the Fe-Ga alloy deposited under a diffusive regime; however, in the ballistic sample, a higher presence of D0 3 /B2 phases is evidenced. Structural characteristics, from local to long range, seem to determine the magnetic behavior of the layers. Whereas a clear in-plane magnetic anisotropy is observed in the film deposited under ballistic flow, the diffusive sample is magnetically isotropic. Therefore, our experimental results provide evidence of a correlation between flow regime and structural properties and its impact on the magnetic behavior of a rather unexplored compositional region of Fe-Ga compounds.

Investigation of the Out of Plane Component of the Magnetization of [Fe72Ga28(x nm)/Tb33Fe67(50 nm)]2 Multilayers

“…We have always found this easy axis along the reference direction that corresponds to the vapor beam direction (Figure ). This is in agreement with previous works in which samples have also been sputtered in the oblique incidence …”

“…The absence of such halo around 32° can be taken as indication of the stoichiometry of our Tb 33 Fe 67 layers. A similar broad halo around 27° can be observed in the XRD patterns of sputtered Fe‐Ga layes with a similar Ga content . We can therefore correlate this broad halo around 27° to the presence of a disordered phase in the Fe‐Ga layers.…”

“…The difference is that the peaks of the Fe‐Ga alloys are shifted to lower angles due to the increase of the lattice parameter upon the introduction of Ga as sustitutional in the Fe matrix. For the Fe‐Ga, the observed diffraction peak can be related to the A2, B2, and D0 3 phases but not the L1 2 . For the as‐grown samples it also appears a rather broad halo around 27°, that points to the presence of a rather disordered structural phase .…”

“…Although a contribution from Mo cannot be completely ruled out, we obtain the diffraction peaks centered at angles around 40.7° being therefore mainly related to Tb 33 Fe 67 . In the case of the Fe 100− x Ga x alloys with a Ga content ≤30 at%, they typically show the same diffraction pattern than α ‐Fe . The difference is that the peaks of the Fe‐Ga alloys are shifted to lower angles due to the increase of the lattice parameter upon the introduction of Ga as sustitutional in the Fe matrix.…”

“…Its decrease indicates its crystallization upon annealing. The sputtering deposition of Fe 100− x Ga x thin films with x ≈ 28 at% promotes the growth of different phases, mainly chemically disordered A2 together with ordered D0 3 and B2 . A2 phase can be kept thanks to rapid cooling processes avoiding the formation of the ordered phases, D0 3 and B2 .…”