Room temperature ferromagnetism in pristine MgO thin films

Abstract

Robust ferromagnetic ordering at, and well above room temperature is observed in pure transparent MgO thin films (<170 nm thick) deposited by three different techniques. Careful study of the wide scan x-ray photoelectron spectroscopy rule out the possible presence of any magnetic contaminants. In the magnetron sputtered films, we observe magnetic phase transitions as a function of film thickness. The maximum saturation magnetization of 5.7 emu/cm3 is measured on a 170 nm thick film. The films above 500 nm are found to be diamagnetic. Ab initio calculations suggest that the ferromagnetism is mediated by cation vacancies.

Resistance switching in transparent magnetic MgO films

“…Moreover, electrical switching that has been observed in MgO films [13] and MgO-based magnetic tunnel junctions [14][15][16] is attributed either to nanostructural rearrangements of metallic ions in the electrode/barrier interfaces or reversible displacement of oxygen vacancies. On the other hand, defect-induced ferromagnetism in MgO has already been observed at room temperature [17][18][19][20][21]. Our previous results demonstrate that the presence of cation vacancies has a strong impact on the electronic properties of MgO.…”

Defect-induced magnetism in undoped wide band gap oxides: Zinc vacancies in ZnO as an example

“…Furthermore, there are two additional reasons leading us to believe that V Zn plays the critical role in establishing the ferromagnetic order: one is that the magnetism was weakened after Ar annealing which is believed to heal the V Zn defects in the as-grown samples. 61 The other evidence comes from the recent reports where cation vacancies was suggested to be responsible in establishing the ferromagnetism in wide band gap oxides, 5,31,40,73 Additionally, many recent theoretical calculations suggest that the s electrons contributed by V O cannot establish ferromagnetism. 27,34 These considerations guided us to focus on the role of V Zn in the first-principles calculations which will be detailed in the next section.…”

“…Indeed, experimental observations of ferromagnetism in ZnO thin films 23 and pure ZnO powders 24,25 have been attributed to the intrinsic defects. It was also proposed that defects like Zn and O vacancies, 23,[26][27][28][29][30][31] [35][36][37][38][39][40][41] suggesting that the underlying physics is universal. However, open questions still remain related to this approach of defect engineering towards magnetism in oxides: e.g., what kinds of defects can contribute magnetic moments?…”

Aging of magnetic properties in MgO films

“…7 The spin polarization of oxygen ions at low-coordinated sites was calculated to increase as site coordination decreases. Figure 1 relates the vacancy concentration to the calculated magnetization values.…”