Unveiling the Different Physical Origins of Magnetic Anisotropy and Magnetoelasticity in Ga-Rich FeGa Thin Films

Abstract

The aim of this work is to clarify how the in-plane magnetic anisotropy and magnetoelasticity depend on the thickness of Ga-rich FeGa layers. Samples with a Fe 72 Ga 28 composition were grown by sputtering in the ballistic regime in oblique incidence. Although for these growth conditions uniaxial magnetic anisotropy could be expected, in-plane anisotropy is only present when the sample thickness is above 100 nm.By means of differential x-ray absorption spectroscopy we have determined the influence of both Ga-pairs and tetragonal cell distortion on the evolution of the magnetic anisotropy with the increase of FeGa thickness. On the other hand, we have used the cantilever beam technique with capacitive detection to also determine the evolution of the magnetoelastic parameters with the thickness increase. In this case, experimental results can be understood considering the grain distribution. Therefore, the different physical origin for anisotropy and magnetoelasticity opens the possibility of independently tune these two characteristics in Ga-rich FeGa films.

Interfacial coupling effect of Cr2O3 on the magnetic properties of Fe72Ga28 thin films

“…We have analyzed the possibility of Fe 72 Ga 28 oxidation because of its growth on top of Cr 2 O 3 , but XRD measurements do not show evidences of oxidation within the resolution technique. The diffraction peaks related to FeGa are similar to what we have previously reported about sputtered Fe 72 Ga 28 thin films being the (110) the main diffraction peak 16 – 19 . For Fe 72 Ga 28 we can determine the lattice parameter ( a ) thanks to Bragg’s law: where is the family of planes, the diffraction angle, and the radiation wavelength (Cu K α in this case).…”

“…Sputtered Fe 72 Ga 28 layers deposited in the ballistic regime develop in-plane magnetic anisotropy above 100 nm 16 , 18 . Nevertheless, the coupling with Cr 2 O 3 completely eliminate this in-plane anisotropy even for thicknesses well above 100 nm (Fig.…”

“…The sputtering deposition was carried out in oblique incidence with an angle between the vapor beam and the perpendicular to the sample of about 25° and a distance of 9 cm between target and substrate. This direction of the vapor beam within the sample plane is taken as the reference direction to control the direction of the in-plane uniaxial anisotropy axis when created 16 , 17 , 38 . Fe 72 Ga 28 films were deposited from a target with a composition of Fe 72 Ga 28 with a diameter of 5 cm and a thickness of 2 mm using an Ar pressure of 3·10 −3 mbar and a growth power of 90 W in all cases.…”

“…FeGa alloys are extensively studied because of their large magnetostriction constant and low coercivity 13 – 16 . Also interesting is the possibility in sputtered Fe 72 Ga 28 layers of controlling the in-plane magnetic anisotropy by growth conditions 17 – 19 or by thermal treatments combined with mechanical stress 20 .…”

Out of plane component of the magnetization of sputtered Fe72Ga28 layers

“…In the last years, there is a huge interest in the metallic FeGa system due to the discovery in 2000 of a large magnetostriction in these free rare-earth alloys [1][2]. Many of the published works have been devoted to the understanding of the origin of this enhanced magnetostriction in contrast with pure Fe [3][4][5][6][7][8][9][10][11][12]. It is remarkable that the largest deformation in Fe can be reached in the [100] direction with a (3/2)100 value of 22 ppm, whereas in FeGa alloys it can be obtained 430 ppm in that same direction [5].…”