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Correlation of Nanoscale Structure and Magnetic Properties in Manganese Doped Germanium Dilute Magnetic Semiconductors Li He1,2, Wenjing Yin1, Jiani Yu1,3, Jiwei Lu1, Stuart Wolf1, and Robert Hull2 1 Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904, U.S.A. 2 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, U.S.A. 3 Present address: Nvidia, Santa Clara, CA 95050, U.S.A. ABSTRACT Spintronic devices generally require the spin of carriers to be utilized in the storage or manipulation of data. One theoretical model for ferromagnetism in dilute magnetic semiconductors (DMS) results from the percolation of ferromagnetic regions around dilute dopants such as Mn atoms in III-V or group IV materials through the interaction of Mn atoms with carriers. Our work employed Mn implantation in Ge with subsequent rapid thermal annealing or TEM in-situ annealing to study the correlation between structure and magnetic properties. The magnetic properties of 300-350 ºC implanted Ge:Mn (which produced crystalline Ge films) varied significantly with implantation dose and annealing condition due to precipitation and transformation of different MnxGe1-x secondary phases. It was found that Mn substitution of Ge and MnxGe1-x secondary phases can both result in ferromagnetic properties. By combining TEM in-situ annealing and ex-situ magnetic characterization, we have demonstrated detailed correlation of magnetic properties with nanoscale structures in Mn implanted Ge DMS materials. INTRODUCTION The essence of spintronic devices- the use of carrier spins to store and transmit information- motivates researchers to find materials where the spin of carriers can be manipulated electrically. Since Park et al. discovered hole-mediated ferromagnetism (FM) in Mn doped Ge [1], great interest has been attached to this material and its FM mechanism. Mn atoms act as acceptors to Ge [1,2]. Each Mn ion has a partially filled outer shell and hence a magnetic moment. At low temperature, the spins of nearby ions interact and align with each other. Moreover, the ion spin is coupled with spins of electrical carriers that are weakly bounded to the ions. These interactions generate magnetic polarons of aligned spins. Neighboring polarons may interact through intermediate carriers. As a result the global magnetic ordering can be achieved. The alignment of spin in and between the clusters and the cluster radius all decrease with temperature since thermal fluctuation tends to break the ordering. Due to low solubility of Mn in Ge (~10-5 % at Ge melting point, 938 ºC [3]), incorporation of Mn in Ge has been through non-equilibrium process, such as molecular beam epitaxy (MBE) growth of Ge:Mn [4-6], and Mn implantation in Ge[7,8]. It is evident that Mn often aggregates into clusters or intermetallic phases and results in significant changes in magnetic properties. For example, Ge:Mn without Mn5Ge3 or Mn11Ge8 phases was generally reported with Curie temperature (TC, transitio