Room temperature ferromagnetism in Mn doped dilute ZnO semiconductor; an electronic structure study

Abstract

Confronting reports of room temperature ferromagnetic ordering in bulk as well as thin films of dilute doped semiconductors motivated us to prepare and study some dilute Mn-doped (2% and 4%) ZnO polycrystalline pellets. Our aim was to find out how the changes in the electronic structure can correlate to the observed magnetic properties in such diluted magnetic semiconductor materials. The 2% Mn sample shows above room temperature magnetic ordering with further enhancement in magnetic properties upon cooling. The magnetic ordering gets completely quenched for 4% Mn doping at room temperature and no evidence of ordering found even down to 5 K. The electronic structure of these two samples has been investigated using Mn L23 X-ray absorption spectroscopy, Zn 2p and 3p, Mn 3p and O 1s X-ray photoemission spectroscopy. Our results show that overall the manganese shifts toward the higher valence state upon Mn doping while there is no change in the zinc and oxygen valence. The concentration of divalent Mn state is found to be much higher in the ferromagnetic sample (Mn=2%). For the non-ferromagnetic sample a larger contribution of higher oxidation Mn states is present and also the oxygen content is found to be higher. These two factors have been correlated to the suppressed ferromagnetism but it is difficult to predict their relative weights.