Observation of Negative Magnetic Hysteresis Loop in ZnO Thin Films

Micah Haseman,Farida A Selim,Sunil Thapa,Armando Hernandez,A M Colosimo,David Winarski,Andreas Wagner,Matt Kusz,Pooneh Saadatkia,Wolfgang Anwand

doi:10.1155/2018/3575917

Abstract

We report on the observation of an unusual negative magnetic hysteresis loop in ZnO thin film codoped with cobalt and aluminum (Co-Al:ZnO), while other transition-metal-doped ZnO films, such as Cu-doped ZnO and Mn-doped ZnO, exhibit normal hysteresis loops. The unusual magnetic behavior is ascribed to the presence of double magnetic layers with different magnetic moments due to the change of structural defects across the film layers. Positron annihilation measurements confirmed the presence of unique microstructural changes in the Co-Al:ZnO film. This study shows that defects in diluted magnetic semiconductors may induce not only ferromagnetism but also novel magnetic behaviors.

Highlights

The increasing potential of ferromagnetic materials as facilitators of spin transport electronics and applications has led to a substantial growth in diluted transition-metal-doped magnetic semiconductor (DMS) research [1,2,3]
We report on the observation of an unusual negative magnetic hysteresis loop in ZnO thin film codoped with cobalt and aluminum (Co-Al:ZnO), while other transition-metal-doped ZnO films, such as Cu-doped ZnO and Mn-doped ZnO, exhibit normal hysteresis loops
Experimental studies on FM in DMS are often irreproducible and contradictory [13, 14], and the ambiguous nature of FM in DMS is obscured by the possible presence of transition-metal precipitates or clusters and further complicated by the magnetic dependence on growth conditions and postgrowth treatments [15,16,17,18,19]; this indicates a strong correlation between intrinsic defects and ferromagnetism, a notion that is supported by observations of ferromagnetism in undoped ZnO [20, 21]

Summary

Introduction

The increasing potential of ferromagnetic materials as facilitators of spin transport electronics and applications has led to a substantial growth in diluted transition-metal-doped magnetic semiconductor (DMS) research [1,2,3]. Experimental studies on FM in DMS are often irreproducible and contradictory [13, 14], and the ambiguous nature of FM in DMS is obscured by the possible presence of transition-metal precipitates or clusters and further complicated by the magnetic dependence on growth conditions and postgrowth treatments [15,16,17,18,19]; this indicates a strong correlation between intrinsic defects and ferromagnetism, a notion that is supported by observations of ferromagnetism in undoped ZnO [20, 21] Due to this dubiety in ferromagnetic origins, a scant number of explanations have been proposed to interpret FM mediation and magnetic moment genesis, complicating the narratives of many magnetic phenomena. The measurements revealed the presence of adjacent layers with different defect structures in Co-Al-doped ZnO film which may lead to different magnetic moments triggering this unusual magnetic behavior

Experimental Details

Results and Discussions

Conclusions