Anisotropic magnetoresistance inGa1−xMnxAs

Abstract

We have measured the magnetoresistance in a series of Ga1−xMnxAs samples with 0.033≤ x ≤ 0.053 for three mutually orthogonal orientations of the applied magnetic field. The spontaneous resistivity anisotropy (SRA) in these materials is negative (i.e. the sample resistance is higher when its magnetization is perpendicular to the measuring current than when the two are parallel) and has a magnitude on the order of 5% at temperatures near 10K and below. This stands in contrast to the results for most conventional magnetic materials where the SRA is considerably smaller in magnitude for those few cases in which a negative sign is observed. The magnitude of the SRA drops from its maximum at low temperatures to zero at TC in a manner that is consistent with mean field theory. These results should provide a significant test for emerging theories of transport in this new class of materials. PACS: 75.50.Pp, 72.20.My, 72.80.Ey, 73.50.Jt The recent discovery of ferromagnetism at temperatures as high as 110K in Ga 1−x Mn x As has greatly broadened the interest in diluted magnetic semiconductors over the past few years [1][2][3]. A large number of groups are now investigating these materials which could form the basis for a wide variety of new magneto-electronic devices that may be grown pseudo-morphically on GaAs. The utility of similar devices has already been established using nano-composite structures based on metallic magnetic materials (the so-called giant magnetoresistance and tunnel junction magnetoresistance [4,5]). The semiconducting materials open up new opportunities as they also introduce the prospects of optical or electronic control of the magnetic properties [6,7].These new materials present many interesting challenges as we embark on efforts to make use of their properties in real devices. These challenges come from both the fundamental point of view (trying to understand their properties and what factors control them) and from the desire to manufacture high quality materials in the face of severe constraints imposed by the possibility of nucleating unwanted phases during growth [2]. These two challenges are intimately connected since the density of carriers is expected to influence such material properties as the Curie temperature and magnetic anisotropy [8,9], but this density is strongly influenced by defects included in the structure as a result of the constraints on the growth conditions.In view of our limited understanding of these materials it is prudent to spend some effort exploring the transport properties of individual material layers in preparation for constructing multilayered structures to form devices. Toward that end, in this article we report on magnetotransport measurements in a series of Ga 1−x Mn x As films (x= 0.033 to 0.053). We concentrate on the dependence of the film resistivity on the orientation of an applied magnetic field in the hope that this dependence might be less sensitive to the details of the disorder in the films than is the resistivity itself.The Mn-alloyed films were...

Out-of-plane magnetization reversal processes of (Ga,Mn)As with two different hole concentrations

“…[8,9,10,11,12] This interpretation agrees well with direct observation of magnetic domain structures and magnetization reversal process, [13] clearly showing that magnetotransport measurement is a suitable tool for studying the magnetization reversal process in III-V MAS even for out-of-plane field orientation we are studying.…”

“…1(b) can be explained by the anisotropic magnetoresistance (AMR). [2,21] As shown in previous work, [8,9,10,11] the AMR of (Ga,Mn)As reflects on a change in the angle between the current direction [100] and the magnetization orientation, and shows the largest value when the magnetization is perpendicular to a current flow. This fact indicates that the MR curve in H ≤ ± 3500 Oe is associated with the magnetization process.…”

“…In order to understand magnetization reversal processes and magnetic domain structures, a number of magnetotransport studies have been reported so far, [7,8,9,10,11,12] where a change in longitudinal resistance in an in-plane magnetic field is well understood using anisotropic magnetoresistace (AMR) and the characteristic magnetic anisotropy in (Ga,Mn)As. [8,9,10,11,12] This interpretation agrees well with direct observation of magnetic domain structures and magnetization reversal process, [13] clearly showing that magnetotransport measurement is a suitable tool for studying the magnetization reversal process in III-V MAS even for out-of-plane field orientation we are studying.…”

Angle-dependent magnetotransport in cubic and tetragonal ferromagnets: Application to (001)- and(113)A-oriented(Ga,Mn)As

“…5,6,7,8 According to Eqs. (8) and (9), however, such differences may be expected even in the case of perfect cubic symmetry due to the (n · m) 2 terms of ρ cubic long .…”

“…Considerable progress has been made in understanding its structural, electronic, and magnetic properties. In particular, anisotropic magnetoresistance (AMR), 4,5,6,7,8,9 planar Hall effect (PHE), 10 and magnetic anisotropy (MA), 11,12,13,14,15,16,17 have been identified as characteristic features, making (Ga,Mn)As potentially suitable for field-sensitive devices and non-volatile memories. These properties have been shown to be governed by several parameters, such as Mn concentration, hole density, strain, or temperature.…”