Room-Temperature Ferromagnetic Ga 1-x Mn x As (x e 0.05) Nanowires: Dependence of Electronic Structures and Magnetic Properties on Mn Content Han Sung Kim, Yong Jae Cho, Kang Jun Kong, Chang Hyun Kim, Gyeong Bok Chung, and Jeunghee Park* Department of Chemistry, Korea UniVersity, Jochiwon 339-700, Korea Jae-Young Kim Pohang Accelerator Laboratory, POSTECH, Pohang 790-784, Korea Jungbum Yoon, Myung-Hwa Jung, † and Younghun Jo Quantum Material Research Team, Korea Basic Science Institute, Daejeon 305-333, Korea Bongsoo Kim Department of Chemistry, KAIST, Daejeon 305-701, Korea Jae-Pyoung Ahn AdVanced Analysis Center, Korea Institute of Science and Technology, Seoul 136-791, Korea ReceiVed December 11, 2008. ReVised Manuscript ReceiVed January 21, 2009 Ga 1-x Mn x As nanowires were synthesized with finely controlled Mn contents (x ) 0, 0.01, 0.02, 0.03, and 0.05) by the vapor transport method. They consisted of single-crystalline GaAs nanocrystals (avg. diameter ) 60 nm) grown along the [111] direction. The Mn doping decreases the lattice constant, most significantly at x ≈ 0.03. X-ray photoelectron spectroscopy revealed that as the Mn content increases, the binding energy of Ga 2p shifts to a higher energy, which can be correlated with the hybridization between the Mn 2+ ions and the holes. X-ray absorption spectroscopy and X-ray magnetic circular dichroism confirmed that the Mn 2+ ions substitute into the tetrahedrally coordinated Ga sites and that the magnetic moment is maximized at x ) 0.03, where the lattice constant is minimized and the binding energy of Ga 2p is maximized. The magnetization measurement revealed that all of these nanowires exhibited room- temperature ferromagnetic behavior, which is also observed most significantly for x ≈ 0.03. 1. Introduction Diluted magnetic semiconductors (DMSs), in which the host cations are randomly substituted by magnetic ions, have attracted a considerable amount of attention because of their excellent potential as key materials for spintronic devices. 1-3 The demonstration of the unique phenomena associated with DMSs, such as the field-effect control of their ferromag- netism, efficient spin injection to produce circularly polarized light, and spin-dependent resonant tunneling, has opened up a rich and various landscape for technological innovation in magnetoelectronics. As one of the most important ferromag- netic DMSs, Mn-doped GaAs (Ga 1-x Mn x As) has been extensively studied for more than two decades. 4-16 The spin 5/2 Mn (Mn 2+ ) ions at the regular sites of the zinc blende lattice of the GaAs host act as acceptors, thus providing both * Corresponding author. E-mail: parkjh@korea.ac.kr. † Present address: Department of Physics, Sogang University, Seoul 121- 742, Korea. (1) (a) Ohno, H. Science 1998, 281, 951. (b) Ohno, Y.; Young, D. K.; Beschoten, B.; Matsukura, F.; Ohno, H.; Awschalom, D. D. Nature 1999, 402, 790. (c) Ohno, H.; Chiba, D.; Matsukura, F.; Omiya, T.; Abe, E.; Dietl, T.; Ohno, Y.; Ohtani, K. Nature 2000, 408, 944. (2) Fiederling, R.; Keim, M.; Reuscher, G.; Ossau, W.; Schmidt, G.; Waag, A.; Molenkamp, L. W. Nature 1999, 402, 787. (3) Wolf, S. A.; Awschalom, D. D.; Buhrman, R. A.; Daughton, J. M.; von Molna´r, S.; Roukes, M. L.; Chtchelkanova, A. Y.; Treger, D. M. Science 2001, 294, 1488. (4) Ohno, H.; Shen, A.; Matsukura, F.; Oiwa, A.; Endo, A.; Katsumoto, S.; Iye, Y. Appl. Phys. Lett. 1996, 69, 363. (5) Oiwa, A.; Katsumoto, S.; Endo, A.; Hirasawa, M.; Iye, Y.; Ohno, H.; Matsukura, F.; Shen, A.; Sugawara, Y. Solid State Commun. 1997, 103, 209. (6) Dietl, T.; Ohno, H.; Matsukura, F.; Cibert, J.; Ferrand, D. Science 2000, 287, 1019. (7) Sanvito, S.; Ordejo´n, P.; Hill, N. A. Phys. ReV.B 2001, 63, 165206. (8) Erwin, S. C.; Petukhov, A. G. Phys. ReV. Lett. 2002, 89, 227201. (9) Jungwirth, T.; Konig, J.; Sinova, J.; Kucˇera, J.; MacDonald, H. Phys. ReV.B 2002, 66, 012402. (10) (a) Mahadevan, P.; Zunger, A. Phys. ReV.B 2003, 68, 075202. (b) Mahadevan, P.; Zunger, A.; Sarma, D. D. Phys. ReV. Lett. 2004, 93, 177201. (11) Bergqvist, L.; Korzhavyi, P. A.; Sanyal, B.; Mirbt, S.; Abrikosov, I. A.; Nordstro¨m, L.; Smirnova, A. E.; Mohn, P.; Svedlindh, P.; Eriksson, O. Phys. ReV.B 2003, 67, 205201. (12) Krstajic´, P. M.; Peeters, F. M.; Ivanov, V. A.; Fleurov, V.; Kikoin, K. Phys. ReV.B 2004, 70, 195215. (13) Schulthess, T. C.; Temmerman, W. M.; Szotek, Z.; Butler, W. H.; Stocks, G. M. Nat. Mater. 2005, 4, 838. (14) Kitchen, D.; Richardella, A.; Tang, J.-M.; Flatte´, M. E.; Yazdani, A. Nature 2006, 442, 436. 1137 Chem. Mater. 2009, 21, 1137–1143 10.1021/cm8033388 CCC: $40.75  2009 American Chemical Society Published on Web 03/02/2009