Magnetocrystalline Anisotropy Enables Field-Free Deterministic Switching in Tm ₃ Fe ₅ O ₁₂ /Pt Bilayers: An Atomistic Spin Dynamics Study

Deterministic and field-free switching of perpendicular magnetization remains a key challenge for scalable and energy-efficient spintronic memory. Here, we employ atomistic spin dynamics simulations to uncover the microscopic mechanism behind the recently observed 3-fold rotation and mirror (3 m ) -symmetric switching in epitaxial (111)-oriented Tm 3 Fe 5 O 12 (TmIG)/Pt bilayers. We show that intrinsic cubic magnetocrystalline anisotropy (MCA) of TmIG spontaneously breaks mirror symmetry along the out-of-plane direction, giving rise to 3 m -symmetric torques that enable deterministic switching without external fields. The switching exhibits strong angular selectivity with respect to crystallographic axes and current direction, and under large spin–orbit torque excitation, coherent terahertz oscillations produce toggle-like switching. Systematic tuning of current density and pulse width allows control over the switching-mode. Comparative simulations on Y 3 Fe 5 O 12 (YIG) confirm that MCA-driven field-free switching is a universal feature of rare-earth iron garnets. These results establish a symmetry-based design principle for ferrimagnetic spintronic devices, with implications for ultrafast, low-power memory and terahertz spintronics.