Characterizing the defects and ferromagnetism in metal oxides: The case of magnesium oxide

Highlights: • Defects in metal oxide materials- highlighting the MgO. • Intrinsic and extrinsic, etc. defects. • Ion implantation, UV-, gamma-, LASER-, swift heavy ion irradiation. • Microscopic studies, EPR and UV–vis spectroscopy, XAS, XMCD, SQUID, VSM, etc. • Synchrotron X-ray radiation investigations for defects. Defects play an essential role in controlling the phenomenon of d0 ferromagnetism in nonmagnetic oxides. Defects can have significant impact on behavior, especially d0 ferromagnetism of oxide materials at room temperature (RT). Defects in magnesium oxide can be created by various phenomena like ion implantation, swift heavy ion/laser/gamma or UV irradiation, etc. This review focuses on the various characterization tools that are helpful to identify the nature of defects in the materials. Microscopic studies infer about the crystal structure modification via doping concentrations in metal oxides. Tools like ultra-violet visible (UV–Vis) spectroscopy and photoluminescence (PL) spectroscopy enrich the information on defects as well as depict the kind of vacancy. Electron paramagnetic resonance (EPR) is suitable to get information on spin centers in the materials. In addition to this, synchrotron radiation-based techniques like X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) are also helpful to know about the structural defects and nature of vacancy in the materials. Vibrating sample magnetometry (VSM)/superconducting quantum interference device (SQUID) measurements deduce the magnetic properties and cause of the ferromagnetism in the metal oxide. Thus, these characterization tools are covered in this review by addressing the origin of defects as well as the methodology utilized to create and control defects in the materials. A detailed understanding of these issues is focused on magnesium oxide, a well-known candidate of the d0 ferromagnetic category.