Ubiquity of ferromagnetic signals in common diamagnetic oxide crystals

Abstract

The magnetic properties of MgO, ${\text{MgAl}}_{2}{\text{O}}_{4}$, ${\text{SrTiO}}_{3}$, ${\text{LaAlO}}_{3}$, LSAT, and ZnO single crystals were investigated. These crystals show three contributions to the magnetization, namely, an intrinsic diamagnetic contribution, a paramagnetic contribution, due to various transition-metal impurities, as well as a ferromagnetic contribution. The latter shows coercive field values that are rather independent of the actual crystal material. The ferromagnetic hysteresis loops of the magnetization per volume suggest a surface contribution. The origin of the ferromagnetic contribution as arising from either defect-induced ferromagnetism or ferromagnetic impurities is discussed.