S. K. Arora,1,* Han-Chun Wu,1 R. J. Choudhary,1,† I. V. Shvets,1 O. N. Mryasov,2 Hongzhi Yao,3 and W. Y. Ching3 1Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN), School of Physics, Trinity College Dublin, Dublin 2, Ireland 2Seagate Research Center, Seagate Technology, 1251, Waterfront Place, Pittsburgh, Pennsylvania 15222, USA 3Department of Physics, University of Missouri-Kansas City, Kansas City, Missouri 64110, USA Received 23 January 2007; revised manuscript received 12 March 2008; published 28 April 2008