Ferromagnetic resonance and control of magnetic anisotropy by epitaxial strain in the ferromagnetic semiconductor (Ga0.8,Fe0.2)

Abstract

We study the strain dependence of the magnetic anisotropy of room-temperature ferromagnetic semiconductor (Ga 1-x ,Fe x)Sb (x = 20%) thin films epitaxially grown on different buffer layers, using ferromagnetic resonance measurements. We show that the magnetocrystalline anisotropy (K i) in (Ga 1-x ,Fe x)Sb exhibits a dependence on the epitaxial strain and changes its sign from negative (in-plane magnetization easy axis) to positive (perpendicular magnetization easy axis), when the strain is changed from tensile to compressive. Meanwhile, the shape anisotropy (K sh) is negative and dominant over K i. Therefore, the effective magnetic anisotropy (K eff = K i + K sh) is always negative, leading to the in-plane magnetic anisotropy in all the (Ga 1-x ,Fe x)Sb samples. This work is the first observation of ferromagnetic resonance and strong shape anisotropy at room temperature in III-V ferromagnetic semiconductors. We also observed very high Curie temperature (T C ≳ 400 K) in p-type (Ga,Fe)Sb, which is the highest T C reported so far in III-V based ferromagnetic semiconductors.

In-plane to perpendicular magnetic anisotropy switching in heavily-Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb with high Curie temperature

“…From these detailed characterizations, we confirmed the intrinsic ferromagnetism of (Ga,Fe)Sb. XRD results show all the (Ga,Fe)Sb films with various thicknesses have tensile strain and almost the same value of epitaxial strain  ~ -1.58 %, consistent with our previous report [32]. Therefore, in this study, we rule out any strain induced magnetic anisotropy change.…”

“…Therefore, by thoroughly investigating the magnetic properties, particularly the magnetic anisotropy, of these Fe-doped FMSs, it is expected to uncover various unknown aspects in the magnetic physics and materials science of FMSs. Previously by studying the MA of (Ga0.8,Fe0.2)Sb thin films (thickness d = 15 nm), we found that IMA is dominant due to the large shape anisotropy constant (Ksh) [32]. Here in this work, we report a new finding that the switching of MA from IMA to PMA can be induced by increasing the thickness of (Ga,Fe)Sb over a critical value of 42 nm.…”

“…We used ferromagnetic resonance (FMR) to estimate the MA constants of the (Ga0.7,Fe0.3)Sb thin films in a similar fashion as reported in our previous work [32]. The samples were placed at the center of a TE011 microwave cavity, at which the rf magnetic field and rf electric field of the microwave are largest and smallest, respectively.…”

“…Moreover, these Fe-doped FMSs, especially (Ga,Fe)Sb, are very promising for room-temperature device applications because of their high TC (TC > 400 K [32]). The observation of high-TC ferromagnetism in these Fe-doped FMSs is striking, because it is opposite to the prediction of the mean-field Zener model [33] which claims that TC will be high (low) in wide-gap (narrow-gap) FMSs.…”

Evolution of Fe 3d impurity band state as the origin of high Curie temperature in the p -type ferromagnetic semiconductor (Ga,Fe)Sb

“…Since the doped Fe ions in the III-V semiconductors are expected to substitute for the cation (In 3+ or Ga 3+ ) sites as Fe 3+ and conducting carriers can be introduced by donor/acceptor doping, off-stoichiometry, and defects, one can independently control the concentrations of Fe ions and carriers in Fe-doped FMSs. Furthermore, the highest TC values reported so far in (In0.65,Fe0.35)Sb (385 K) 21 and (Ga0.8,Fe0.2)Sb (> 400 K) 25 are well above room temperature. Considering these advantages, Fe-based FMSs are more promising materials for practical semiconductor spintronics devices operating at room temperature.…”