Hole-mediated ferromagnetism in GaN doped with Cu and Mn
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Hole‑mediated ferromagnetism in GaN doped with Cu and Mn G. Guzmán1 · D. Maestre2 · M. Herrera1 Received: 17 April 2020 / Accepted: 22 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract We present a cathodoluminescence (CL) and superconducting quantum interference device (SQUID) magnetometry study of the generation of ferromagnetism (FM) in GaN doped with non-magnetic (copper) and magnetic (manganese) impurities. Our results suggest that p–d hybridization between Cu and N ions promotes FM in GaN:Cu, and that an exchange interaction between the Cu2+ (d9) orbitals and the t2g anti-bonding orbitals of Mn2+ ions generates FM in GaN:Cu and GaN:Mn. Besides that, the exchange interaction is mediated by holes, created by the acceptor nature of the impurities Cu2+ and Mn2+, and of the point-defects-type gallium vacancies (VGa) present in samples. For this study, we synthesized undoped GaN, GaN:Cu, and GaN:Mn samples by thermal evaporation onto Ni0.8Cr0.2/Si substrates in a horizontal furnace operated at low vacuum. Energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) measurements confirmed that the obtained samples consisted of GaN without residual oxide phases. XPS measurements also revealed the coexistence of C u+ and C u2+ ions in the GaN:Cu sample, and M n2+ in the GaN:Mn sample. CL spectra from Cu and Mn-doped GaN samples showed that doping generates a relative intensity enhancement of two bands centered at 2.60 and 3.00 eV, associated with the formation of VGa in GaN. Magnetization–applied field (M–H) curves of the GaN, GaN:Cu, and GaN:Mn samples revealed a FM behavior at room temperature.
1 Introduction Since Dietl et al. [1] predicted the ferromagnetic behavior above room temperature of GaN doped with low concentrations of Mn, the interest in using this semiconductor in the spintronic field has markedly increased [1]. However, because ferromagnetism (FM) has also been demonstrated in GaN doped with magnetic and non-magnetic impurities [2–8], as well as in undoped GaN [9,10], its origin in GaN and other dilute magnetic semiconductors (DMS) still remains controversial. Conventional super-exchange and double-exchange interactions do not adequately explain the long-range magnetic order observed for magnetic impurities at low concentrations. Exchange interactions mediated by the point-defects present in semiconductors have been
* M. Herrera [email protected] 1
Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, 22800 Ensenada, Baja California, Mexico
Departamento de Física de Materiales, Facultad de CC. Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
2
proposed to explain the FM behavior, consequently, many efforts have been devoted to control the formation of pointdefects during intentional and non-intentional impurification of GaN [11–15]. Therefore, as it is very probable that ferromagnetism is generated in DMS by exchange interactions mediated by
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