Field‐Free Magnetization Switching Driven by Spin–Orbit Torque in L1₀‐FeCrPt Single Layer

Abstract

Electrical switching of magnetization through spin-orbit torque (SOT) induced by a composition gradient in single-layer L1 0 -FePt has garnered considerable research interest owing to its inherent superior perpendicular magnetic anisotropy (PMA) that provides ultrahigh capacity to magnetic storage and memory devices. However, a large in-plane external magnetic field is typically required to assist SOT-driven switching, which is still a limitation for the practical application of L1 0 -FePt. This study reports realizable field-free magnetization switching by SOT via Cr doping to form a singlelayer magnetic structure with an in-plane magnetization component oriented toward L1 0 -FeCrPt [110] direction that strongly depends on the magnetocrystalline anisotropy. The Cr doping yields a considerable in-plane exchangecoupling effective field that is conducive toward disintegrating the rotational switching symmetry and facilitates field-free switching in single-layer films with PMA. Furthermore, this in-plane effective field exhibits a nonmonotonic evolution with respect to the Cr-doping concentration, which is validated using first-principles calculation with a frustration-based model of magnetic exchange interactions. Thus, this study delivers an attractive method to facilitate the field-free electrical manipulations of magnetization in singlelayer ferromagnets to motivate innovative designs for advanced spintronics devices.

Switching of Perpendicular Magnetization by Spin–Orbit Torque

“…Recently, experiments have established that a strong bulk-type net damping-like spin-orbit torque (Figure 15a) can be generated within single-crystalline GaMnAs with bulk inversion asymmetry [46] and some thick, strong spin-orbit coupling magnetic single layers, e.g., Co1-xPtx, [52,114,115] Fe1-xPtx, [53,120,121] Fe1-xTbx, [54] Co1-xTbx, [122,152] GdFeCo, [116,153] and L10-FeCrPt. [154] Switching of perpendicular magnetization by such bulk SOTs has been demonstrated. For example, Liu et al [54] reported bulk SOT switching of 20 nm Fe0.42Tb0.58 layer with a giant anisotropic field of 36.8 kOe, high coercivity of 1.72 kOe and moderate magnetization of 134 emu/cm 3 at a low current density of 5.5×10 6 A/cm 2 under an in-plane longitudinal magnetic field of ±3 kOe (Figure 15b).…”

“…In conventional spin‐current generator/magnet (SCG/M) bilayers ( Figure a) the efficiency of the damping‐like spin–orbit torque ($$\xi _{DL}^j$$) is usually low, particularly when θ SH is small and when T int is far less than unity due to spin memory loss [ 153–161 ] and spin backflow [ 149,162–166 ] (e.g., $$\xi _{DL}^j$$ ≈ 0.05–0.15 for Pt/3 d ferromagnet [ 16 ] ). A more critical limitation of the bilayer scheme is that the efficiency of the damping‐like SOT per magnetic layer thickness ( t ), $$\xi _{DL}^j$$/ t , is inversely proportional to t .…”

“…In conventional spin-current generator/magnet (SCG/M) bilayers (Figure 16a) the efficiency of the damping-like spin-orbit torque (𝜉 j DL ) is usually low, particularly when 𝜃 SH is small and when T int is far less than unity due to spin memory loss [153][154][155][156][157][158][159][160][161] and spin backflow [149,[162][163][164][165][166] (e.g., 𝜉 j DL ≈ 0.05-0.15 for Pt/3d ferromagnet [16] ). A more critical limitation of the bilayer scheme is that the efficiency of the damping-like SOT per magnetic layer thickness (t), 𝜉 j DL /t, is inversely proportional to t. This degrades the effectiveness of the interfacial SOTs in spintronic applications where the M has to be thick to maintain a bulk [54,139,167] or shape [168,169] perpendicular magnetic anisotropy (PMA) and/or thermal stability when the lateral size scales down to tens of nanometers (e.g., magnetic tunnel junctions and racetrack nanowires).…”

Frontiers in all electrical control of magnetization by spin orbit torque

“…Similar to exchange bias in FM/AFM, the pseudo-exchange bias between two FMs is also an effective approach to introduce interface effective magnetic field [79,80]. Apart from this, structural asymmetry can introduce tilted PMA of the FM, effectively enabling all electrical deterministic SOT switching [81][82][83][84].…”

Engineering Symmetry Breaking Enables Efficient Bulk Spin‐Orbit Torque‐Driven Perpendicular Magnetization Switching

“…Recently, the novel bulk SOT (BSOT) effect has attracted intensive research interest because it can break through the interfacial nature of conventional SOT in NM/FM bilayer structures, and simultaneously implement high Δ and low J c . [16][17][18][19][20][21] The BSOTinduced magnetization switching has been demonstrated in single magnetic layers, such as GaMnAs with globally or locally broken inversion symmetry. But it is detrimental to practical applications due to the requirement of low temperature.…”