Nat. Mater., 2019, doi: 10.1038/s41563-019-0365-9
The emerging field of spintronics aims at the utilization of both the spin and charge of electrons, and the combination semiconducting and magnetic properties within a single material. Magnetic oxide semiconductors are significant spintronics materials. Besides of doping the semiconducting materials with a certain concentration of transition metals to integrate ferromagnetism into semiconductors, it is found that oxides of non-magnetic cations exhibit elusive signs of weak temperature-independent ferromagnetism, namely “d0 ferromagnetism”. Up to now, a major research effort has been devoted to obtain ferromagnetism and explore the related mechanisms. Anyway, as the initial enthusiasm for magnetic oxides ebbed, with no encouraging sign of useful spintronics functionality, scientists tended to dismiss the magnetism as some sort of dirt effect or measurement artefact. Interest in unidentified magnetic objects waned. The publications on this subject declined rapidly.
Recently, in a comment, Professor J. M. D. Coey suggests that magnetism in d0 oxides is associated with surface defects, but it defies conventional explanation. He outlines two hypotheses to explain d0 magnetism, which are a spin-split defect impurity band and giant orbital paramagnetism related to zero-point vacuum fluctuations, respectively. He gives a few examples of d0 oxides and points out the way forward including experiments designed to test which hypothesis, if either, is correct, and standard first-principles approaches to calculate electronic structure of surface defects, and band formation in the presence of natural adsorbates. At the same time, the practical implications are also mentioned.
Xiaohong Xu (Shanxi Normal University, Linfen, China)