Structural Effects of Transition Metal Oxide Calcinations on Wurtzite Type Semiconductors That are Ferromagnetic at Room
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Structural Effects of Transition Metal Oxide Calcinations on Wurtzite Type Semiconductors That are Ferromagnetic at Room Temperature Peter Moeck1, Lori Noice1, Chunfei Li1, Amita Gupta2, Rolf Erni3,4, Nigel D. Browning3,5, and K.V. Rao2 1 Portland State University, Portland, OR, 97201 2 Royal Institute of Technology, Stockholm, 100 44, Sweden 3 University of California, Davis, CA, 95616 4 University of Antwerp, Antwerp, 2020, Belgium 5 Lawrence Livermore National Laboratory, Livermore, CA, 94550 ABSTRACT Gallium nitride powders and zinc oxide powders were each calcined with a few weight percent of copper oxide and/or magnesium oxide either in air or N2. Powder X-ray diffractometry, transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy were performed in order to observe calcination induced structural effects on these wurtzite type semiconductors. We note that our earlier magnetic results on Cu doped GaN are qualitatively consistent with recent first principle calculations [Wu et al., Appl. Phys. Lett. 89 (2006) 62505].
INTRODUCTION In confirmation of Dietlís and coworkerís well known prediction that wide band-gap semiconductors with wurtzite structure may possess Curie temperatures above room temperature when doped with transition metals [1], some of the authors of this paper reported ferromagnetism (at and above room temperature) for both ZnO doped with manganese [2,3] and GaN doped with copper [4-6]. Both superconducting quantum interference device magnetometry and ferromagnetic resonance measurements were employed at and above room temperature to confirm the ferromagnetism unambiguously by two different methods in two different laboratories [2,5,6]. Besides inducing the ferromagnetism, the calcination process caused structural effects on the wurtzite type semiconductors. Since some of these effects could turn out to be relevant for the optimization of calcination processes, this paper summarizes selected (and previously unpublished) results of our observations of such effects by means of powder Xray diffractometry (XRD), high-resolution phase-contrast transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and energy dispersive X-ray spectroscopy (EDXS) in the scanning probe mode (STEM) on such samples [3-6]. The calcination parameters that led to ferromagnetism at room temperature in wurtzite GaN are explicitly given.
EXPERIMENTAL DETAILS All powder sample preparations were preformed at The Royal Institute of Technology in Stockholm where appropriate amounts of constituent powders were combined by weight percent, pressed into pellets and calcined in air or under N2. There were three samples of ìZnO powdersî: ZnO calcined simultaneously with 2 % MnO2 and 2 % CuO, ZnO calcined with 2 % CuO, and ZnO calcined 4 % CuO. Each calcination was for 8 hours at 673 K followed by 12 hours at 773 K in air. There were also ten samples of ìGaN powdersî: nominally pure GaN from the same supplier that was used for preparing the other
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