Above Room-Temperature Ferromagnetism in GaN Powders by Calcinations with CuO
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0941-Q08-14
Above Room-Temperature Ferromagnetism in GaN Powders by Calcinations with CuO Lori Noice1, Bjoern Seipel1, Rolf Erni2,3, Amita Gupta1,4, Chunfei Li1, peter Moeck1, Venkat Rao4, and Nigel Browning2,5 1 Department of Physics, Portland State University, Portland State University, P.O.Box 751, Portland, OR, 97207-0751 2 Department of Chemical Engineering and Materials Science, University of California at Davis, University of California at Davis, One Shields Avenue, Davis, CA, 95616 3 FEI Electron Optics, PO Box 80066, 5600 KA Eindhoven, Netherlands 4 Department of Materials Science, The Royal Institute of Technology, Tmfy-MSE, The Royal Institute of Technology, Brinellvägen 23, Rm 224, SE 100 44, Stockholm, Sweden 5 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720 ABSTRACT
Gallium nitride powders were calcined with copper oxide in either air or N2 and analyzed by means of powder X-ray diffraction (XRD), high-resolution parallel illumination (HRTEM) and scanning probe transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDXS), and electron energy loss spectroscopy (EELS) in order to address the structural and electronic effects of Cu-incorporation into GaN. Gallium oxide and multiple copper oxide phases corresponding to the calcination environment were detected. Significant changes in the lattice parameters and electronic structure of the N2-processed GaN indicate incorporation of both copper and oxygen into the GaN lattice as well as changes in the chemical bonding due to the calcinations process. SQUID magnetometer measurements at 300 K demonstrated ferromagnetism in selected samples. INTRODUCTION
Prospects for a more advanced spintronic technology, one which integrates intrinsic magnetic and electronic functionality into a single material, have provoked intensive research towards the development of dilute magnetic semiconductors (DMS) with above roomtemperature ferromagnetism [1]. In 2000, the mean-field Zener model of ferromagnetism was used by Dietl et al. to predict above room temperature Curie temperatures (TC) for two semiconductors, GaN and ZnO, when doped with 5 % Mn and with a hole density of 3.5 x 1020 cm-3 [2]. Since that time, ferromagnetism above room temperature has been reported on bulk and thin film samples of Mn-doped GaN [3]. Room temperature ferromagnetism has also been achieved for Mn-doped ZnO [4], and recently, ferromagnetism at 300 K has been reported in Cudoped ZnO as well [5]. However, the potential of Cu-doped GaN as a high TC DMS remained largely unexplored. In an effort to address this latter issue, this paper summarizes our structural and spectroscopic characterization of GaN calcined with CuO for 4 hours in a N2 atmosphere [6], and includes characterizations of additional samples of GaN calcined with CuO in both air and N2 for 40 hours. For several samples, magnetization versus applied magnetic field hysteresis curves demonstrating ferromagnetism at 300 K are shown for the first ti
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