Effect of hydrogen on magnetic properties in MgO studied by first-principles calculations and experiments

We investigated the effects of both intrinsic defects and hydrogen atom impurities on the magnetic properties of MgO samples. MgO in its pure defect-free state is known to be a nonmagnetic semiconductor. We employed density-functional theory and the Heyd-Scuseria-Ernzerhof (HSE) density functional. The calculated formation energy and total magnetic moment indicated that uncharged V-Mg(0) and singly charged V-Mg(-1) magnesium vacancies are more stable than oxygen vacancies Mg (V-O) under O-rich growth conditions and introduce a magnetic moment to MgO. The calculated density of states (DOS) results demonstrated that magnetic moments of V-Mg result from spin polarization of an unpaired electron of the partially occupied valence band, which is dominated by O 2p orbitals. Based on our calculations, V-Mg is the origin of magnetism and ferromagnetism in MgO. In contrast, the magnetic moment of the magnetic V-Mg-MgO crystal is suppressed by hydrogen (H) atoms, and unpaired electrons are donated to the unpaired electronic states of V-Mg when the defect complex H-i-V-Mg is formed. This suggests that H causes a reduction in magnetization of the ferromagnetic MgO. We then performed experimental studies to verify the DFT predictions by subjecting the MgO sample to a thermal treatment that creates Mg vacancies in the structure and intentionally doping the MgO sample with hydrogen atoms. We found good agreement between the DFT results and the experimental data. Our findings suggest that the ferromagnetism and diamagnetism of MgO can be controlled by heat treatment and hydrogen doping, which may find applications in magnetic sensing and switching under different environmental conditions.