Spin-wave resonances and surface spin pinning inGa1−xMnxAsthin films

Abstract

We investigate the dependence of the spin-wave resonance ͑SWR͒ spectra of Ga 0.95 Mn 0.05 As thin films on the sample treatment. We find that for the external magnetic field perpendicular to the film plane, the SWR spectrum of the as-grown thin films and the changes upon etching and short-term hydrogenation can be quantitatively explained via a linear gradient in the uniaxial magnetic anisotropy field in growth direction. The model also qualitatively explains the SWR spectra observed for the in-plane easy-axis orientation of the external magnetic field. Furthermore, we observe a change in the effective surface spin pinning of the partially hydrogenated sample, which results from the tail in the hydrogen-diffusion profile. The latter leads to a rapidly changing hole concentration/magnetic anisotropy profile acting as a barrier for the spin-wave excitations. Therefore, short-term hydrogenation constitutes a simple method to efficiently manipulate the surface spin pinning.

The essential role of carefully optimized synthesis for elucidating intrinsic material properties of (Ga,Mn)As

“…A more than an order of magnitude experimental scatter and a lack of any clear trend as a function of Mn doping can be found in the previous literature for the Gilbert damping and spin stiffness constants (Supplementary Note 3) [19][20][21][22][23][24][25][26][27][28] . Significant variations can be also found in the experimental magnetic anisotropy constants of (Ga,Mn)As (ref.…”

Systematic study of the spin stiffness dependence on phosphorus alloying in the ferromagnetic semiconductor (Ga,Mn)As

“…The spin stiffness constant can be extracted from the frequency spacing of excited modes. One technique is the standard ferromagnetic resonance (FMR), 4,17 another is the time-resolved magnetooptical Kerr effect experiment (TRMOKE) 6,16,18,19 recently pointed out as an optical analog of FMR for DMS. 19 However, experimentally some modes undetectable by FMR are observed by TRMOKE as will be shown further on.…”

“…1 More fundamentally, DMS and more specifically the III-V based (Ga,Mn)As have become in the past decade a benchmark material in order to achieve predictable tuning of magnetic properties. Levers such as the temperature, 2 the carrier concentration 3,4 but also the strain applied on the magnetic layer 5,6 or alloying with phosphorus 7,8 have been used in order to change the micromagnetic properties, e.g., the Curie temperature T C , the saturation magnetization M s , and the magnetic easy axis.…”

SWR Studies of Higher-Order Surface Anisotropy Terms in (Ga,Mn)As Thin Films

“…Although in our considerations here we have referred to (Ga,Mn)As thin films magnetically homogeneous throughout the bulk (and therefore described by the surface inhomogeneity model), we believe that the expected correspondence between bulk and surface in terms of magnetocrystalline anisotropy applies as well to volume-inhomogeneous (Ga,Mn)As thin films in which SWR is observed. This is the case of the samples studied by Goennewein et al [6,9,10] and Khazen [28], which use the volume inhomogeneity model for the interpretation of their results; we believe that also their SWR spectra bear a significant imprint of the surface anisotropy too. Thus, it can be expected that the surface anisotropy of such samples can be studied also by a method similar to that proposed in the present paper, based on SWR spectra measured in various carefully chosen angular configurations.…”

“…Particularly, the magnetic anisotropy of thin films of gallium manganese arsenide, (Ga,Mn)As, is one of their most interesting properties, since it determines the direction of the sample magnetization, the manipulation of which is of key importance for prospective application of this material in memory devices. For this reason the magnetic anisotropy of (Ga,Mn)As thin films is being intensively investigated by many experimental techniques; these include spin-wave resonance (SWR) [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. It is worthy of notice that the main objective of the SWR studies conducted so far in (Ga,Mn)As has been to obtain information on certain volume characteristics, such as the value of uniaxial anisotropy [9] or exchange constant [16] in the studied material.…”