Combinatorial Synthesis and Characterization of CoMnGe Alloys
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Combinatorial Synthesis and Characterization of CoMnGe Alloys Frank Tsui,a Liang He, and Lei Ma Dept. of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599, U.S.A. a Email: [email protected] ABSTRACT Ternary alloys of CoMnGe have been synthesized and characterized using combinatorial molecular beam epitaxy techniques. Structural evolution was studied using real-time scanning reflection high-energy electron diffraction, and magnetic properties were probed using magnetooptic Kerr effect imaging and SQUID magnetometry. Growth and properties on several substrate orientations were explored. These alloys exhibit a rich variety of magnetic and magnetooptic behavior, including a robust phase near Co2MnGe with high spin polarization, Tc, and magnetooptic response. The observed magnetic responses show strong correlation with structural transformations, such that structural ordering leads to enhanced magnetism. The observed magnetic behavior and the alloys’ compatibility with Ge and Si substrates make them potential candidates for spin electronic transport studies and applications. INTRODUCTION Magnetic alloys are fundamentally interesting and technologically important, because they offer a wide range of novel structures and properties that are not present in elemental materials, including magnetic semiconductors,1 half-metals,2 bulk metallic glasses.3 Heterostructures of these systems may provide key materials systems for the development of new magnetic device concepts. The exciting prospect of studying these materials is to be able to tailor experiments in order to explore specific properties, such as specific structure-property relationships. However, the large number of combinations and the nontrivial composition dependent structural and magnetic phase diagrams have also made them difficult to study, particularly using the traditional one sample at a time approach that is not only tedious and time consuming but also not sensitive to abrupt changes and phase boundaries. New approaches and techniques are necessary for exploring these systems systematically, so that properties can be screened rapidly and efficiently and intricate interactions between structures and properties can be elucidated. In this paper we describe application of combinatorial approach to conventional molecular beam epitaxy (MBE) synthesis and characterization of multicomponent alloys, and we use a ternary film system, CoMnGe, as an example to illustrate the approach and to highlight what can be done with it. The alloy system is chosen because novel half-metallic ferromagnetism has been predicted in it 2 and its potential compatibility with standard semiconductor substrates. In the following sections we first describe combinatorial MBE synthesis and characterization, particularly the approach of “continuous phase diagramming” (CPD), and then present some of our findings on epitaxial films of CoMnGe grown on Ge. COMBINATORIAL SYNTHESIS AND CHARACTERIZATION Combinatorial synthesis was carried out using an advanced MBE system. A
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