Hole-mediated ferromagnetism in GaN doped with Cu and Mn

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 Cu+ and Cu2+ ions in the GaN:Cu sample, and Mn2+ 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.