Ordered arrangements of selective-area grown MnAs nanoclusters as components for novel, planar magneto-electronic devices

摘要

Novel concepts such as racetrack memory devices or planar logic elements based on ferromagnetic materials are subject of today’s research. However, there are certain limits which will have to be faced by the established technology. A very attractive model kit for planar magneto-electronic devices can be found in Manganese arsenide (MnAs ) nanoclusters grown by selective-area metal-organic vapor-phase epitaxy (SA-MOVPE). MnAs exposes ferromagnetism at room temperature and below, and the growth on GaAs wafers provides the integrability into III-V based concepts, which play a huge role in the modern semiconductor research and industry. The SA-MOVPE growth technique allows a highly precise control of the size, shape and position of the grown MnAs nanocluster structures. The presented work gives a short overview of the material system and the applied synthesis and analysis techniques as well as of related physical concepts. Magnetoresistance (MR) measurements are performed on planar, single MnAs nanoclusters and cluster arrangements. In addition, the influence of thermal effects on the observed phenomena is evaluated.It has been found that a GMR-like spin valve characteristics is realized in an arrangement of two elongated, clearly separated nanoclusters connected by a gold layer. This observation is further explained considering the special magnetic anisotropy conditions in elongated MnAs nanoclusters, which is described using an energy landscape comprising magnetocrystalline and shape anisotropy as well as coupling effects between the clusters and to the external magnetic field.Besides the first observation of a spin-valve behavior in a MnAs nanocluster arrangement, the influence of thermal energy on the MR behavior has been a major part of the presented work. In numerous measurements, a high amount of spontaneous MR jumps occurred which could not be related to any recurring external influences and thus had to be explained by internal processes. The investigation of two compact, merged nanocluster arrangements over a longer measurement time with constant external parameters allowed a quantitative approach to this issue, since the observed resistance jumps occurred between recurring resistance levels.