First-principles study of enhancement of perpendicular magnetic anisotropy obtained by inserting an ultrathin LiF layer at an Fe/MgO interface

Perpendicular magnetic anisotropy (PMA) is a key property of magnetoresistive random access memory (MRAM). To increase areal density of MRAM it is important to find a way to enhance the PMA. Recently a strong enhancement of the PMA by inserting an ultrathin LiF layer at an Fe/MgO interface was reported [T. Nozaki et al., NPG Asia Materials (2022) 14: 5]. To understand the origin of the observed enhancement of the PMA we perform first-principles calculations of magnetocrystalline anisotropy energy (MAE) of the following four kind of multilayer structures: Fe/MgO, Fe/LiF/MgO, Fe/FeO/MgO, and Fe/FeF/LiF/MgO. We find that the MAEs of the Fe/LiF/MgO and the Fe/FeF/LiF/MgO structures are almost the same as that of the Fe/MgO structure, while the MAE of the Fe/FeO/MgO structure is less than a half of that of the Fe/MgO structure. The results show that the major origin of the enhancement of the PMA obtained by inserting an ultrathin LiF layer at an Fe/MgO interface is the suppression of the mixing of Fe and O atoms at the interface. We also find that the in-plane Fe-F coupling gives a positive contribution to the MAE while the in-plane Fe-O coupling gives a negative contribution. The results are useful for designing of high-PMA materials.

Automated summary

Recent research has shown that the perpendicular magnetic anisotropy (PMA) of magnetoresistive random access memory (MRAM) can be significantly enhanced by inserting an ultrathin LiF layer at an Fe/MgO interface. First-principles calculations revealed that the PMA enhancement is mainly due to the suppression of Fe and O atom mixing at the interface. Additionally, in-plane Fe-F coupling contributes positively to the magnetocrystalline anisotropy energy (MAE), while Fe-O coupling has a negative contribution. These findings are valuable for the design of high-PMA materials.