Evidence of Carrier Mediated Ferromagnetism in GaN:Mn/GaN:Mg Heterostructures
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Evidence of Carrier Mediated Ferromagnetism in GaN:Mn/GaN:Mg Heterostructures F. Erdem Arkun1, Mason J. Reed1, Erkan Acar Berkman1, Nadia A. El-Masry1, John M. Zavada2, M. Oliver Luen3, Meredith L. Reed3, Salah M. Bedair3. 1Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, 27695 2Army Research Office, Research Triangle Park, Durham, North Carolina, 27709 3Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina, 27695 ABSTRACT Dilute Magnetic Semiconductors (DMS's) posses a strong potential to make use of the spin of carriers in spintronic devices. Experimental results and theoretical calculations predict that GaN:Mn is a potential semiconductor material for spintronic device applications. The dependence of the room temperature ferromagnetic properties of GaN:Mn/GaN:Mg double heterostructures (DHS) on the Fermi level position in the crystal is demonstrated. Several GaN:Mn/GaN:Mg DHS are grown by metal organic chemical vapor deposition on sapphire. It is shown that initially paramagnetic films can be rendered ferromagnetic by facilitating carrier transfer through the GaN:Mn/GaN:Mg interface. Additionally, it is demonstrated that ferromagnetism depends on the thickness of the GaN:Mn and GaN:Mg layers. The carrier transfer process essentially changes the Fermi level position in the crystal. By choosing the right thicknesses for GaN:Mn and GaN:Mg an optimum DHS that exhibits room temperature ferromagnetism is grown. An identical structure, with the exception of insertion of an AlGaN barrier in order to obstruct the carrier transfer at the interface, results in paramagnetic films for AlGaN barriers thicker than 25nm. These results are explained based on the change in the occupancy of the 3d-Mn impurity band, and indicate that carrier mediation is the possible mechanism for the ferromagnetism observed in the MOCVD grown GaN:Mn material system. This is the first evidence that this material system responds to electronic perturbations, hence ferromagnetism observed is not due to secondary phases or spin glass behavior. INTRODUCTION The origin of ferromagnetism in perovskite structures of manganese has been attributed to the indirect coupling of the d-shells via conducting electrons[1]. Also, it is known that the spin correlation of a single transition metal atom, as part of a crystal, is no different than that of an atom isolated in a gaseous state. The lowest energy configuration occurs when the d-shell has the highest net electron spin i.e. all spins of the unpaired electrons point in the same direction. Interest in achieving ferromagnetic semiconductors has led to the investigation of the mechanisms that stabilize ferromagnetism (FM) in transition metal-doped semiconductors. Among the III-V semiconductors investigated to achieve ferromagnetism, GaMnN is the most prominent semiconductor in which the FM phase is stabilized over other non-magnetic phases [2]. A model proposed by Dietl et. al. [3] predicts a Cur
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