Complex domain-wall dynamics in compressively strainedGa1−xMnxAsepilayers

Abstract

The domain-wall-induced reversal dynamics in compressively strained Ga 1−x Mn x As was studied employing the magneto-optical Kerr effect and Kerr microscopy. Due to the influence of a uniaxial part in the in-plane magnetic anisotropy 90°Ϯ ␦ domain walls with considerably different dynamic behavior are observed. While the 90°+ ␦ reversal is identified to be propagation dominated with a small number of domains, the case of 90°−␦ reversal involves a larger number of nucleation centers. The domain-wall nucleation/propagation energies ⑀ for both transitions are estimated using model calculations from which we conclude that single domain devices can be achievable using the 90°+ ␦ mode.The discovery of the ferromagnetic semiconductor Ga 1−x Mn x As and the possible implementation into spintronic devices triggered great interest in understanding its fundamental properties. 1 The linkage between carrier density and magnetic properties in this hole-mediated ferromagnet allows tuning of its magnetic properties such as the Curie temperature ͑T c ͒ upon changing the carrier concentration. 2,3 In addition, magnetic domain-wall ͑DW͒ logic operations may be implemented 4 including magnetoresistive read-outs. However, any application in this direction requires full control over magnetic reversal dynamics, which in most cases happens via the nucleation and propagation of domain walls.A good understanding of the magnetic anisotropy landscape is also required not only for the design of magnetoresistive devices but also because magnetic anisotropy can manifest in the domain-wall dynamics. The magnitude of the magnetic anisotropy is related to important parameters such as the domain-wall energy and width, 5 which can determine a process to be propagation or nucleation dominated. This can be very well visualized in the effect of a nonuniform anisotropy distribution in simulated reverse domain patterns. 6 So far, domain-wall studies by means of Kerr microscopy ͑KM͒ in Ga 1−x Mn x As have been mostly performed in films with tensile strain where the magnetization pointed perpendicular to the plane. 7 Ga 1−x Mn x As with in-plane magnetization has been extensively studied using magnetotransport measurements. 8,9 However, this technique does not provide spatially resolved information about DW nucleation and propagation processes. In this study we present the direct observation of DW motion in compressively strained Ga 1−x Mn x As by KM and the dependence of the DW dynamics on the direction of the applied magnetic field. While an earlier magneto-optical study in the literature 10 did not address possible anisotropies in the DW dynamics, our KM results reveal a distinct anisotropy in the DW dynamics dependent on the direction of the applied magnetic field with respect to the crystal axes. From the analysis of angleresolved magneto-optical Kerr effect ͑MOKE͒ measurements, we attribute this anisotropy to the existence of two different types of DWs. All measurements were done on Hall bar devices of 150 m width, patterned in ͓110͔ and ͓110͔ direc...

Temperature-dependent Néel wall dynamics in GaMnAs/GaAs

“…Very recently single DWs have been resolved in the static limit by means of electron holography on the scale of a few micrometers [6] with high spatial resolution. In contrast, we have shown that Kerr microscopy provides full time and spatially resolved information on the dynamics of in-plane magnetic domains during the magnetization reversal on the scale of a few hundred micrometers [7]. Due to the low Curie-temperatures T c well below room temperature of most ferromagnetic semiconductors like GaMnAs it is of technical interest to study these materials in the highest possible temperature range just below T c .…”

Magneto-optical Kerr spectroscopy of (Ga,Mn)(As,P) ferromagnetic layers: Experiments and k.p theory

“…17 Using the time-resolved MOKE, laser pump-probe experiments enable the investigation of magnetization dynamics in the femtosecond to nanosecond range, in particular, the coherent collective magnetic excitations. 6,18,19 Magneto-optical microscopy uses the MOKE to gain insight into the magnetic domains static pattern 7,20,21 and the domain wall dynamics. 22 While the MO effects in (Ga,Mn)As have been extensively investigated, [13][14][15][16][23][24][25][26][27][28][29][30][31][32][33][34] the MO properties of (Ga,Mn) (As,P) thin films, more specifically the interplay between the Mn doping and P substitution, remain to be investigated.…”

Magnetoelectric properties of oxygenated (Ga,Mn)As

“…The (Ga,Mn)As samples used in this work were grown by molecular beam epitaxy (MBE) on a semi-insulating GaAs substrate. 9 The manganese concentrations in the samples employed, designated A and B, are 1.2% and 3%, with thicknesses 170 and 40 nm, respectively. Magnetotransport measurements have been carried out using 30-μm-wide Hall bar devices patterned along the hard [110] direction by standard photolithography.…”