MAGNETISM AND MAGNETOTRANSPORT STUDIES OF IV-VI FERROMAGNETIC SEMICONDUCTOR

LIM SZE TER

Publication

MAGNETISM AND MAGNETOTRANSPORT STUDIES OF IV-VI FERROMAGNETIC SEMICONDUCTOR

LIM SZE TER

Abstract

Among the IV-VI ferromagnetic semiconductors, GeMnTe reveals relatively high Curie temperature (Tc) of 200 K under appropriate growth conditions. This makes it a promising material for spintronic applications and warrants much research interests. This thesis focuses on the study of magnetic and transport properties of GeMnTe thin films grown by molecular beam epitaxy. Anomalous Hall effect is clearly observed in the samples which can be attributed to extrinsic skew scattering. The interplay between localized magnetic moments from the Mn ions and the free carriers resulting from the presence of both Ge vacancy and Ge-Te disorder type of defects determine the ferromagnetic properties in GeMnTe. This interaction is investigated by means of magnetotransport studies in GeMnTe under the effect of hydrostatic pressure (P). The Tc is observed to change with P which is due to the increase in carrier concentration responsible for the interactions between Mn ions. A two valence model as well as RKKY interaction are invoked to explain these results. Magnetoresistance (MR) measurements have been used to investigate the localization and antilocalization effects. The spin-orbit, elastic and inelastic scattering times as well as coherence length as a function of pressure are obtained from the fitting of MR results. Additionally, exchange bias effect (EB) of GeMnTe with antiferromagnetic MnTe and MnO materials has been investigated. While GeMnTe-MnTe system only leads to a modification of coercivity field, a negative EB shift in the hysteresis loop is observed for GeMnTe-MnO bilayer when it is cooled in applied field. Our findings pose challenges as well as opportunities for future studies of GeMnTe for spintronic applications.