PNNL

Abstract

Sparked by theoretical predictions for p-type ZnO, CoxZn1-xO (Co:ZnO) is one of the most favoured materials within the search for a doped semiconductor with ferromagnetic properties at room temperature—an essential prerequisite for spintronics. Despite early experimental reports of high temperature ferromagnetism, mainly based on measurements performed with superconducting quantum interference device (SQUID),the experimental findings become more and more controversial. Recent reports claim a paramagnetic behavior of the Co-sublattice or suggest extrinsic origins of the observed ferromagnetism. Here we present studies on Co:ZnO samples with nominally 10% cobalt content grown either by magnetron sputtering or pulsed laser deposition (PLD). Since we have recently shown that the dopant behaves purely paramagnetic in case of high structural perfection achieved by PLD growth [6], we focus in this work on structural and magnetic differences of the latter to films produced by reactive magnetron sputtering (RMS). Some reports consider native oxygen vacancies of ZnO as a possible origin of ferromagnetic-like behaviour, therefore we study the magnetic properties of samples which were intentionally grown under a reduced oxygen partial pressure.