Abstract
We report a systematic study of room-temperature ferromagnetism (RTFM) in pristine MgO thin films in their amorphous and nano-crystalline states. The as deposited dc-sputtered films of pristine MgO on Si substrates using a metallic Mg target in an O2 containing working gas atmosphere of (N2 + O2) are found to be X-ray amorphous. All these films obtained with oxygen partial pressure (PO2) ~10% to 80% while maintaining the same total pressure of the working gas are found to be ferromagnetic at room temperature. The room temperature saturation magnetization (MS) value of 2.68 emu/cm3 obtained for the MgO film deposited in PO2 of 10% increases to 9.62 emu/cm3 for film deposited at PO2 of 40%. However, the MS values decrease steadily for further increase of oxygen partial pressure during deposition. On thermal annealing at temperatures in the range 600 to 800 °C, the films become nanocrystalline and as the crystallite size grows with longer annealing times and higher temperature, MS decreases. Our study clearly points out that it is possible to tailor the magnetic properties of thin films of MgO. The room temperature ferromagnetism in MgO films is attributed to the presence of Mg cation vacancies.
Highlights
Magnesium Oxide with rocksalt-structure has been extensively investigated due to its exceptional properties, such as chemical inertness, high electrical resistivity, optical transparency, and low thermal conductivity [1,2,3,4]
In order to understand the origin of the ferromagnetism (FM) observed in MgO films more clearly we investigated the effect of oxygen partial pressure during deposition on the magnetization of
The results indicates that PO2 in working gas plays an important role to determine the magnetic properties of MgO films and ferromagnetism may originate from the defects at the cation sites, which is consistent with the theoretical results [19,30]
Summary
Magnesium Oxide with rocksalt-structure has been extensively investigated due to its exceptional properties, such as chemical inertness, high electrical resistivity, optical transparency, and low thermal conductivity [1,2,3,4]. The role of defective sites in MgO films is a subject of intense research. Such defective sites, present in MgO, can introduce new electronic states, resulting in several intriguing optical, electronic and magnetic phenomena [12,13]. Ferrari et al investigated the magnetic properties of MgO, extensively and suggested that magnetic moment appeared in the local environment of low coordinated
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