Abstract

In the last couple of years, dilute magnetic semiconductor (DMS) has drawn significant interest in the scientific community. Primarily this is due to its potential for application in spintronic devices. The euphoria acquired momentum following the theoretical prediction that diamagnetic ZnO can be made ferromagnetic even at room temperature by doping with transition metal (TM) ions such as Mn. The exact nature of the ferromagnetic coupling of spins in such materials is a matter of debate. Actually the impurity phase assisted ferromagnetism is not intended. The observed ferromagnetism should definitely be intrinsic. Claims and counterclaims in this issue are the key of this debate. However, one important understanding has evolved that defects play crucial role in stabilizing the ferromagnetic state in DMS systems. Some kind of defects or disorder favors ferromagnetism and others compete with this phenomenon. An effort will be made to present the contemporary scenario of research in this field.

So far as discussion of synthesis of TM doped ZnO is concerned both bulk pellet and films will be investigated. Emphasis will be made for development of TM doped ZnO nanostructured samples. Low cost simple synthesis route of formation will be highlighted for its cost-effectiveness in comparison to sophisticated physical methods.

A thorough investigation will be made for characterization of the samples. Structural, morphological, electrical, optical and the most crucial magnetic properties of TM doped ZnO will be discussed. So far as magnetic properties are concerned a careful analysis will be made from the results of field and temperature-dependent dc magnetization measurements and further from ac susceptibility measurement. The correlation between defects and observed intrinsic ferromagnetism of the samples, the crucial role of valence state of TM in achieving intrinsic ferromagnetism and the analysis of X-ray photoelectron spectroscopy data that is crucial in determining valence state of TM will be discussed.

Energetic ion beam irradiation is an efficient tool for introducing defect states in solid materials particularly for semiconductors. There is a wide range of studies of ion irradiation effects on TM doped ZnO. Actually controlled formation of defects along the trajectory of the ion beam modifies chemical and physical properties of the specimens. A careful attempt will be made to explore that formation of defects by ion beam irradiation somehow favors in achieving intrinsic ferromagnetism in the samples or not, since proper correlation of defects and magnetic properties of TM doped ZnO samples can really enhance the potential of this field of scientific research.

To develop TM doped ZnO as a perfect DMS system, synthesis and characterization have to be done in a very specific way. Controlled formation of defects is a key in case of synthesis and ion beam irradiation can be manifested suitably in this respect. Characterization of defects for TM doped ZnO would be given prior importance to unfold the role they play.

Keywords: ZnO, Diluted magnetic semiconductor, Structural and magnetic properties of solids, Ion beam irradiation, Defects.