Abstract
A set of r.f. sputter deposited ZnO thin films prepared with different Mn doping concentrations have been characterised by Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Spectroscopy (XANES) measurements at Zn, Mn and O K edges and at Mn L2,3 edges apart from long range structural characterisation by Grazing Incident X-ray Diffraction (GIXRD) technique. Magnetic measurements show room temperature ferromagnetism in samples with lower Mn doping which is however, gets destroyed at higher Mn doping concentration. The results of the magnetic measurements have been explained using the local structure information obtained from EXAFS and XANES measurements.
Highlights
X-ray Absorption Near Edge Spectroscopy (XANES) measurements at the O K edges and Mn L2,3 edges of the Mn doped ZnO samples were performed at room temperature in the total electron yield (TEY) mode at the soft X-ray absorption spectroscopy (SXAS) beamline (BL-01) of the Indus-2 synchrotron radiation source at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, India
XANES and Extended X-ray Absorption Fine Structure (EXAFS) measurements have been performed at Zn, Mn and O K edges and
XANES results at Mn site confirm the presence of Mn in +2 oxidation state while EXAFS results at Zn and Mn sites confirm that Mn substitutes Zn in ZnO lattice with indication of Mn clustering at relatively higher Mn doping concentration
Summary
The spin-transport properties in Dilute Magnetic Semiconductors (DMS) have many possible potentially interesting device applications.[1,2,3,4,5] Spintronic devices such as spin-valve transistors, spin light-emitting diodes, non-volatile memory, logic devices, optical isolators and ultrafast optical switches are some of the areas of interest for introducing the ferromagnetic properties at room temperature in a semiconductor.[6,7] Doped ZnO is one of the promising DMS materials that simultaneously exhibit ferromagnetic and semiconductor properties and have immense potential in spintronic device application.[2,8,9] Research on doped ZnO systems (both in thin film and bulk form) gained pace since the theoretical prediction by Dietl et al.[2] that 5% Mn doped ZnO could exhibit room temperature (RT) ferromagnetism (FM) followed by theoretical demonstration by Sato and Katayama-Yoshida[9] that ZnO doped with transition metals like Fe, Co and Ni would show ferromagnetic ordering. A wide variation exists in the results reported by various researchers in the literature and the origin of ferromagnetism in these DMS thin film systems is still an open question, whether FM arises due to uniformly distributed TM cations in the semiconductor lattice or due to precipitation of metallic clusters in a homogeneous ZnO host matrix[26] or due to the presence of an entirely separate magnetic phase[27] or due to defects[18] is still to be resolved. In the present study we have performed XAFS measurements on Mn doped ZnO thin films at Zn, Mn and O K edges to probe the local structures surrounding the respective element
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