Synthesis and characterization of single-phase Mn-doped ZnO

Abstract

Different samples of Zn 1-x Mn x O series have been prepared by conventional solidstate sintering method. It has been identified, up to what extent of doping enable us to synthesize single-phase polycrystalline Mn doped ZnO samples which is one of the prerequisite for dilute magnetic semiconductor and we have analyzed its certain other physical aspects. In synthesizing the samples proportion of Mn varies from 1 at% to 5 at%. However the milling times have been varied (6, 12, 24, 48 & 96 hours) for only 2 at% Mn doped samples while for other samples (1, 3, 4 & 5 at% Mn doped) the milling time has been kept fixed at 96 hours. Room temperature X-Ray diffraction (XRD) data reveal that all of the prepared samples up to 3 at% of Mn doping exhibit wurtzite-type structure, no segregation of Mn and/or its oxides has been found. The 4 at% Mn doped samples show a weak peak of ZnMn 2 O 4 apart from usual other peaks of ZnO and the intensity of this impurity peak has been further increased for 5 at% of Mn doping. So beyond 3 at% doping single-phase behavior is destroyed. Band gap for all the 2 at% Mn doped samples have been estimated as between 3.21 to 3.19 eV and reason for this low band gap values has been explained through the grain boundary trapping model. The room temperature resistivity measurement shows increase of resistivity up to 48 hours of milling and with further milling it saturates. The defect state of these samples has been investigated by using positron annihilation lifetime (PAL) spectroscopy technique. Here all the relevant lifetime parameters of positron i.e. free annihilation (τ 1 ), at defect site (τ 2 )and average (τ av ) increases with milling time.

Defects induced ferromagnetism in Mn doped ZnO

“…The sintered material has been milled again for the remaining two third of the total milling time. [28]. So in the present study, the doping level of Mn has etc) is FM at RT [16,29].…”

“…Mn doped ZnO pellet samples have been synthesized by solid-state reaction technique [2,28]. High purity ZnO (99.99%, Sigma-Aldrich, Germany) and MnO 2 (99.9%, Sigma-steps have been carried out for sample synthesis.…”

Magnetic properties of Mn doped ZnO: the role of synthesis route

“…2 at% Mn doped ZnO samples had been prepared in different forms such as thin films [4], bulk-polycrystalline [6] and nanocrystalline [7] samples. The properties (magnetic and other physical properties) of Mn doped ZnO system synthesized by different techniques and in different forms may differ sometimes.…”

“…The properties (magnetic and other physical properties) of Mn doped ZnO system synthesized by different techniques and in different forms may differ sometimes. There are reports of successful achievement of room temperature ferromagnetism in bulk polycrystalline [6] as well as thin films [4] of Mn doped ZnO. However paramagnetism was reported for Mn doped ZnO thin films prepared by using magnetron sputtering technique [8].…”

“…These reports [4,[6][7][8][9][10][11][12][13][14][15] indicate that magnetic properties of Mn doped ZnO systems are highly sensitive to synthesis techniques and conditions such as annealing temperature, annealing atmosphere etc. Apart from TM doping into the ZnO crystal structure, defects play crucial role in stabilizing the FM state.…”