Tailoring Interlayer Chiral Exchange by Azimuthal Symmetry Engineering

Jui-Hsu Han^1*, Yu-Hao Huang¹, Wei-Bang Liao¹, Chen-Yu Hu¹, Yan-Ting Liu¹, Suu-Yen Huang², Chi-Feng Pai¹

¹Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan
²Department of Physics, National Taiwan University, Taipei, Taiwan

* Presenter:Jui-Hsu Han, email:F10527099@ntu.edu.tw

The deterministic switching of spin–orbit torque magnetic random-access memory (SOT-MRAM) with perpendicular magnetic anisotropy (PMA) typically requires an external magnetic field to break the structural symmetry. Achieving field-free switching, therefore, demands an alternative mechanism capable of generating an out-of-plane spin torque. Recently, the interlayer Dzyaloshinskii–Moriya interaction (IL-DMI) in double ferromagnetic layer systems has emerged as a promising route. This chiral exchange interaction induces orthogonal coupling between magnetic layers, enabling coherent and deterministic magnetization switching.
In this work, we demonstrate that IL-DMI can be engineered through azimuthal symmetry control using a wedge deposition technique in both PMA-PMA and PMA–IMA (in-plane magnetic anisotropy) heterostructures. Both configurations successfully achieve field-free switching. By systematically varying the azimuthal deposition direction, we measure the angular dependence of IL-DMI from hysteresis loop offsets measured under different wedge orientations. The offset-angle relation follows a cosine dependence, indicating that the D-vector direction directly governs the IL-DMI strength (denoted as HDMI). Furthermore, we observe additive and subtractive behaviors of HDMI between different wedge geometries, offering a versatile pathway for tuning interlayer chiral coupling.
To address spatial nonuniformity arising from thickness gradients, we further introduce a “counter-wedge” design that compensates for the gradient while preserving a finite IL-DMI. Electrical and magnetic characterizations across a 3-inch wafer reveal improved uniformity in both switching properties and resistivity, confirming the robustness of the counter-wedge configuration.
Our findings demonstrate that azimuthal symmetry engineering provides a powerful strategy to tailor interlayer chiral exchange interactions, enabling field-free SOT switching and paving the way toward the scalability of energy-efficient spintronic memory devices.

Keywords: interlayer exchange interaction, Spin-Orbit Torque, MRAM, field-free switching, Dzyaloshinskii–Moriya interaction