X-ray spectroscopic study of the charge state and local ordering of room-temperature ferromagnetic Mn-doped ZnO

Abstract

The charge state and local ordering of Mn doped into a pulsed laser deposited single-phase thin film of ZnO are investigated by using x-ray absorption spectroscopy at the O K-edge, Mn K-edge and L-edge, and x-ray emission spectroscopy at the O K-edge and Mn L-edge. This film is ferromagnetic at room temperature. EXAFS measurement shows that Mn(2+) replaces the Zn site in tetrahedral symmetry, and there is no evidence for either metallic Mn or MnO in the film. Upon Mn doping, the top of O 2p valence band extends into the bandgap, indicating additional charge carriers being created.

X-ray absorption spectroscopy of Mn doped ZnO thin films prepared by rf sputtering technique

“…The peak position is also shifted to higher energy side with Mn doping. The peak at A is attributed to transition to O2p-Mn3d hybrid state with little contribution from fully occupied Zn 3d shell though it may have some contribution from Zn 4s states also as has been suggested by Guo et al 37 The other significant observation from O K edge XANES spectra is that at position C a small peak is present in case of undoped ZnO sample which becomes very weak for 1% Mn doped ZnO and is absent for all other doping concentrations. However the peak intensity at D is found to continuously increase with increase in Mn doping concentration.…”

“…The O K edge spectra of ZnO obtained here matches well with earlier experimental results. 18,[36][37][38][39] The four main structural features in the spectra are denoted by A, B, C and D. The structural feature denoted by B is attributed mainly due to transition of K shell electron to O 2p hybridization with highly dispersive Zn 3d4s/Mn 3d states which forms the bottom of the conduction band. 36 The intensity and position of the peak observed at B is found to be the same for all doping concentrations.…”

“…The Mn L 2,3 EXAFS spectra of the samples are shown in figure 9 which matches with that reported in the literatures. 37,39,40 The L 3 edge is a result of Mn 2p3/2 -3d transition and L 2 edge is the result of Mn2p1/2-3d transition. Since these transitions involve outer shells of Mn, the change in the oxidation state is more pronounced for L 2,3 edges than for Mn K edge.…”

Mixed Zn and O substitution of Co and Mn in ZnO

“…Refs. [2][3][4][5][6]8) An important consequence of the previous paragraph is that O-substitution can thus explain the observed 4+ charge state of minority fractions of Mn impurities in ZnO thin films. 4,14,15 Moreover, the fact that for those studies the impurities were not incorporated by ion implantation but during growth, indicates that minority anion substitution may be a general phenomenon in transition metal doped ZnO.…”

“…2-4 for Co and Refs. 5-7 for Mn, incorporated either during growth [2][3][4][5][6]8 or by ion implantation. 7,9 When secondary phase segregation is avoided, all 3d TMs, including Co and Mn, were always found to substitute Zn, independently of the growth method, 10 as expected from the chemical similarities between the impurities and the host elements.…”