Magnetocrystalline Anisotropy Enables Field-Free Deterministic Switching in Tm3Fe5O12/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 (3m) -symmetric switching in epitaxial (111)-oriented Tm3Fe5O12 (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 3m-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 Y3Fe5O12 (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.