Magnetic Anisotropy, Spin Pinning, and Exchange Constants of (Ga,Mn)As Films

Abstract

We present a detailed investigation of exchange-dominated nonpropagating spin-wave modes in a series of 100 nm Ga1−xMnxAs films with Mn concentrations x ranging from 0.02 to 0.08. The angular and Mn concentration dependences of spin wave resonance modes have been studied for both as-grown and annealed samples. Our results indicate that the magnetic anisotropy terms of Ga1−xMnxAs depend on the Mn concentration x, but are also strongly affected by sample growth conditions; moreover, the magnetic anisotropy of Ga1−xMnxAs films is found to be clearly linked to the Curie temperature. The spin wave resonance spectra consist of a series of well resolved standing spin-wave modes. The observed mode patterns are consistent with the Portis volume-inhomogeneity model, in which a spatially nonuniform anisotropy field acts on the Mn spins. The analysis of these exchange-dominated spin wave modes, including their angular dependences, allows us to establish the exchange stiffness constants for Ga1−xMnxAs films.

Comparison of micromagnetic parameters of the ferromagnetic semiconductors (Ga,Mn)(As,P) and (Ga,Mn)As

“…A linear or sublinear dependence of the resonant fields on the mode index has been reported also in the other FMR measurements of thick (Ga,Mn)As epilayers [25,26,43,48,49]. The extracted values of the spin stiffness constant D from all available magnetic resonance [26,43,44,49] data in (Ga,Mn)As materials, complemented by values inferred from magnetization and domain studies [46,47], are scattered over more than an order of magnitude and show no clear trend as a function of Mn doping or other material parameters of the (Ga,Mn)As FM semiconductor (see Fig. 12 in Ref.…”

“…Exceptions are the PSSW modes of a uniform thin-film ferromagnet for which the spin stiffness parameter D is directly obtained from the measured resonant fields (see below). There are many reports of SWR measurements in (Ga,Mn)As on >100-nm-thick epilayers using FMR [26,43,48,49]. The modes with H n ∼ n 2 were observed only in a 120-nm-thick, 8% Mn-doped (Ga,Mn)As for magnetic fields applied close to the magnetic EA [43].…”

Magnetic excitations in ferromagnetic semiconductors

“…Along with FMR investigations, spin wave resonance spectra have also been observed in various samples [5,16,17]. In particular, the SWR spectra observed on our samples (with thicknesses in the range from 100 to 200 nm) exhibited certain universal features, illustrated by the data in Figs.…”

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.…”