Control of Magnetic Anisotropy in(Ga,Mn)Asby Lithography-Induced Strain Relaxation

Abstract

We obtain control of magnetic anisotropy in epitaxial (Ga,Mn)As by anisotropic strain relaxation in patterned structures. The strain in the structures is characterized using sophisticated X-ray techniques. The magnetic anisotropy before patterning of the layer, which shows biaxial easy axes along [100] and [010], is replaced by a hard axis in the direction of large elastic strain relaxation and a uniaxial easy axis in the direction where pseudomorphic conditions are retained. This strong anisotropy can not be explained by shape anisotropy and is attributed solely to lattice strain relaxation. Upon increasing the uniaxial strain anisotropy in the (Ga,Mn)As stripes, we also observe an increase in magnetic anisotropy.PACS numbers: 75.50. Pp, 75.30.Gw The (Ga,Mn)As material system has been the focus of many studies over the last years. As the understanding of its complex transport and magnetic properties increases, the focus of interest shifts from basic research towards its application in devices. For this, it is necessary to understand how different parameters influence the ferromagnetic material in structures at the device level. In this letter we present a systematic study of the role of strain relaxation as the dominating factor contributing to the magnetic anisotropy in (Ga,Mn)As nanostructures. A (Ga,Mn)As layer grown epitaxially on a GaAs substrate is subject to compressive strain in the plane of the sample and typically exhibits biaxial in-plane easy axes along [100] and [010], at temperatures around 4 K [1, 2]. In earlier studies, control of the magnetic anisotropy has been achieved by modifying the strain in the layer. Tensile strain can be imposed on the (Ga,Mn)As by growing it on a thick, plastically relaxed (In,Ga)As buffer with a larger lattice parameter, and results in an out-of-plane easy axis [3,4].Here, we follow an alternative approach in modifying the lattice strain of (Ga,Mn)As on GaAs by lithography, which allows us to locally control the magnetic anisotropy of the material. By structuring a fully pseudomorphic 70 nm (Ga,Mn)As layer into thin, elongated stripes, we allow anisotropic, elastic strain relaxation perpendicular to the long axis of the stripe. To increase the strain in the structure compared to the case of (Ga,Mn)As on GaAs, a second sample is processed which includes a highly compressively strained layer acting as an extra stressor to the overlying (Ga,Mn)As layer. The uniaxial strain relaxation in the structures is investigated by grazing incidence X-ray diffraction (GIXRD) and high-resolution X-ray diffraction (HRXRD). To determine the influence of patterning on the magnetic anisotropy, a series of magnetometric and magnetotransport studies are performed. We also present finite-element simulations of anisotropic strain relaxation and k ·p calculations which confirm the relationship between the structural and magnetic behavior observed in our samples.The samples are grown in a dedicated III-V MBE chamber with effusion cells for Ga, In, Mn, and a valved As 4 cell. A 200 nm thic...

GaMnAs-based hybrid multiferroic memory device

“…Lithographically induced unidirectional lateral relaxation can be used to select the easy axis. 16,17 In addition to the large in-plane crystalline anisotropy, there is a uniaxial anisotropy between the ͓110͔ and the ͓110͔ directions which is probably due to the underlying anisotropy of the reconstructed GaAs surface. 18 We use this magnetocrystalline anisotropy in combination to the magnetostrictive effect to demonstrate a bistable memory device.…”

Uniaxial Strain Controlling Magnetic Anisotropy in (Ga,Mn)As

“…This effect was observed experimentally in Refs. [5,6]. Again, opposite behaviour occurs at low hole densities (see Fig.…”

“…Numerous previous studies have shown that magnetocrystalline anisotropy in (Ga,Mn)As is tunable by changing the level of Mn doping, hole density, temperature, or growth strain [1][2][3][4]. Recently, the possibility of breaking the in-plane symmetry of a sample using post-growth patterning has been demonstrated [5][6][7]. In this work we theoretically investigate the effect of lithographically induced uniaxial strain on magnetic anisotropy of narrow (Ga,Mn)As stripes grown on GaAs substrate for a range of hole densities and typical experimental geometries.…”

Magnitude and sign control of lithography-induced uniaxial anisotropy in ultra-thin (Ga,Mn)As wires

“…4 Lithography-induced uniaxial anisotropy due to the magnetostriction effect has been observed in relatively thick ͑Ga,Mn͒As wires on GaAs. [10][11][12][13][14][15] Since the lithographyinduced anisotropy can be externally modulated by changing the wire width 15 after the crystal growth, it enables the switching of the magnetization of ͑Ga,Mn͒As by an electric field with adjusted uniaxial anisotropy in combination with lithography-induced uniaxial anisotropies.In this Letter, we prove the presence of the lithographyinduced uniaxial anisotropy in 1-m-wide ultrathin ͑Ga,Mn͒As wires and also propose that this effect can assist in the electrical manipulation of magnetization.Devices were fabricated from a single wafer consisting of 5-nm-thin ͑Ga 0.94 ,Mn 0.06 ͒As grown on a semi-insulating GaAs substrate. Since the lattice constant of ͑Ga,Mn͒As is larger than that of GaAs, a compressive strain is built into ͑Ga,Mn͒As, which induces an in-plane magnetic easy axis.…”

“…4 Lithography-induced uniaxial anisotropy due to the magnetostriction effect has been observed in relatively thick ͑Ga,Mn͒As wires on GaAs. [10][11][12][13][14][15] Since the lithographyinduced anisotropy can be externally modulated by changing the wire width 15 after the crystal growth, it enables the switching of the magnetization of ͑Ga,Mn͒As by an electric field with adjusted uniaxial anisotropy in combination with lithography-induced uniaxial anisotropies.…”