Self‐organization and finite size effects in epitaxial ferromagnetic MnAs films on GaAs

Abstract

The self-organized striped structure of coexisting α-MnAs and β-MnAs, characteristic for MnAs films grown on GaAs(001) by molecular beam epitaxy under As-rich conditions at low temperature, has been studied in samples prepared under conditions closer to the equilibrium. Whereas the period of the stripe pattern is independent on the preparation procedure, the width of the ferromagnetic α-MnAs stripes increases. Thus, the aspect ratio p between the stripe width L and the stripe thickness t can be varied over a wide range. The magnetic properties of the finite-size magnetic system are investigated as a function of the ratio p at room temperature. The transition from type-I domains with meander-like contrast in the magnetic force microscopy (MFM) image to type-II domains with a line-shaped contrast due to the division of the stripe into N subdomains across the stripe occurs at p ratios expected from a model based on the shape anisotropy. Besides the well-known N = 3 type-II domains also type-II domains with N = 4, 5 were detected. When the stripe width approaches the period of the self-organized structure, the boundary between two neighboring stripes is imaged as chessboard-like contrast in the MFM pattern. The shape of the magnetic hysteresis loops changes with the p ratio or, in other words, with the predominance of inplane or out-of plane magnetic moments in the demagnetized state.

Low energy Ne ion beam induced-modifications of magnetic properties in MnAs thin films

“…Different temperatures correspond to different typical sizes of the α-phase regions that favor different domain types that are presented in Fig. 4 (see also [19,23,26,27,29]). When the ferromagnetic regions are sufficiently extended, the magnetic domains are normally aligned along the easy magnetization axis MnAs [11 20] with the formation of type-I magnetic domains, with meander-like contrast.…”

“…Because of the absence of applied external field, MFM images correspond to the visualization of the out-of-plane magnetic field component from α-phase regions separated by β-phase regions. Different temperatures correspond to different typical sizes of the α-phase regions that favor different domain types that are presented in figure 4 (see also [19,23,26,27,29]). When the ferromagnetic regions are sufficiently extended, the magnetic domains are normally aligned along the easy magnetization axis MnAs( ¯) 1 1 2 0 with the formation of type-I magnetic domains, with meander-like contrast.…”

“…In the past years, many studies have been dedicated to the characterization of epitaxial MnAs films [4,[8][9][10][11][12][13][14][15][16][17]. In particular, magnetic force microscopy (MFM) appeared to be a very useful tool to study the local magnetic properties as a function of different parameters such as: growing conditions [18,19], film thickness [20][21][22], temperature [23][24][25][26], applied magnetic field [27,28] and more recently, applied magnetic field and temperature at the same time [29]. In addition to the above investigations based on the out-of-plane magnetic leak field detection, measurement of the in-plane magnetic component imaging has been obtained on cleavage edges [30].…”