First principles study of perpendicular magnetic anisotropy in thin-film Co₂MnSi

Abstract

Among different physical parameters taken into account for practical implementations in the field of spin-based electronics (spintronics), magnetocrystalline anisotropy (MCA) and spin polarization play a particularly important role. The former determines the orientation of magnetization direction, while a high degree of the latter is required for producing a spin-polarized current, a cornerstone of spintronics. Due to the miniaturization of the modern electronic devices, one often needs to consider physical effects associated with reduced geometry. In particular, in magnetic thin-film materials, MCA may take a form of perpendicular magnetic anisotropy (PMA), which could be beneficial, e.g. in magnetoresistive random-access memory (MRAM). Yet, combining PMA with half-metallicity may be a challenging task, since the latter is usually destroyed in thin-film geometry (e.g., due to the emergence of surface states), while the former is most pronounced in reduced geometry, because of the contribution to MCA from surface anisotropy. Here, we theoretically explore the nature of PMA in the thin-film full Heusler alloy Co 2 MnSi. This material was extensively studied in the past, and it is one of the first compounds for which a half-metallic electronic structure was experimentally confirmed. In addition, it has been reported that this alloy may exhibit perpendicular magnetic anisotropy in thin-film geometry. Here, by analyzing the site-projected magnetocrystalline anisotropy energy (MAE), we confirm that both PMA and surface half-metallicity are very sensitive to the termination surface and mechanical strain. In particular, while MnSi-termination under compressive strain may retain both 100% spin-polarization and out-of-plane magnetization orientation, Co-termination has a detrimental impact on both. These results may serve as a guide for practical applications in the field of spin-based electronics.

Preparation and Magneto-Structural Investigation of Nanocrystalline CoMn-Based Heusler Alloy Glass-Coated Microwires

“…The main features of the magneto-structural properties of Co 2 MnSi glass-coated microwires comes from the fabrication process where Co 2 MnSi Heusler compounds prepared with different form and technique (thin films, bulk and ribbons) does not show similar magneto-structural behavior at the same conditions [11][12][13][14][15][16]. As we described above, the main peculiarity of the Taylor-Ulitovsky method for preparing Heusler-alloy-based glass-coated microwires is the simultaneous rapid solidification of the metallic nucleus surrounded by the glass coating [24,27,47].…”

“…Among Heusler alloys based on 3d transition elements (especially, Co), Co 2 MnSi is of particular interest for advanced spintronic devices because of its large bandgap for minority spins (0.5 to 0.8 eV), high Curie temperature (~985 K), high tunnel magnetoresistance, large magnetoresistance ratios and perpendicular magnetic anisotropy [11][12][13][14]. Both the experimental and theoretical investigation conducted on Co 2 MnSi over the last two decades have been focused on the structural and magnetic properties and their relation to spin polarization [11,[15][16][17].…”

Strain and voltage control of the magnetic anisotropy in Co2MnSi thin film

“…Munira et al reported that Co 2 MnSi/MgO films have perpendicular anisotropy, which is related to Mn-O bonding near the Heusler alloy layer/MgO interface [16] and has been proven by experiment [17]. Later, the termination surface and mechanical strain on the PMA in free-standing thin-film Co 2 MnSi were investigated by firstprinciples study [18]. Despite these studies, there has been little investigation on the voltage and strain effects on the MA of Co 2 MnSi.…”

Effect of Annealing on the Magnetic Properties of Co2MnSi-Based Heusler Alloy Glass-Coated Microwires

“…As a result, Co-based Heusler compounds are gaining the interest of the scientific community, and extensive studies and investigations have been carried out. Co 2 MnSi is a strong option for an advanced spintronic device, because of its high band gap for minority spins (0.5 to 0.8 eV), high Curie temperature (985 K), high tunnel magnetoresistance, large magnetoresistance ratios, and perpendicular magnetic anisotropy [17][18][19][20]. In the last two decades, both experimental and theoretical research on Co 2 MnSi have concentrated on the examination of its structural and magnetic characteristics and on their relationship to spin polarization [21][22][23].…”