Heavy-Ion Radiation Effects on Perpendicular Magnetic Anisotropy Spin–Orbit Torque Magnetic Random Access Memory Thin Films

Abstract: This work investigates heavy-ion irradiation effects on magnetic heterostructure thin-film stacks with constitute core functional building blocks for spin–orbit torque magnetic random-access memory (SOT-MRAM). Perpendicular magnetic anisotropy (PMA) SOT-MRAM thin-film stacks were irradiated with 25 MeV/u Kr ions over a series of ion fluences. Current-in-plane tunneling (CIPT) measurements reveal that the tunneling magnetoresistance (TMR) remains nearly unaltered up to a fluence of 5×10¹¹ ions/cm², while the resistance-area product (RA) fluctuates within a narrow range without exhibiting a systematic trend. At the highest fluence of 1 × 10¹² ions/cm², TMR decreases by only ∼5%, demonstrating robust electronic-transport performance of these thin-film stacks under low-to-moderate irradiation fluences. Alternating-gradient magnetometer (AGM) measurements reveal substantial increases in both saturation magnetization and remanent magnetization following irradiation, while coercivity decreases monotonically with rising fluence. This finding indicates that heavy-ion irradiation can modify magnetization-reversal dynamics and magnetic-domain pinning behavior. Transmission electron microscopy (TEM) characterizations show that the most prominent microstructural alterations occur within the MgO-containing region and its adjacent interfaces. Under high-fluence irradiation, MgO lattice fringes become disordered, atomic intermixing is enhanced across the MgO/CoFeB interface, and the Mg-containing interfacial region broadens; the full width at half-maximum (FWHM) of the Mg elemental distribution increases from 1.48 ± 0.15 nm to 1.76 ± 0.19 nm. In contrast, the CoFeB ferromagnetic layers retain relatively stable structural and compositional properties. All experimental results presented here were obtained from unpatterned PMA SOT-MRAM thin-film stacks; these material-level results cannot be directly extrapolated to the radiation reliability of patterned functional SOT-MRAM devices or arrays. This study provides experimental evidence at the material level for understanding the irradiation response of PMA SOT-MRAM stacks and offers practical guidelines for interface and tunnel-barrier optimization toward radiation-hardened SOT-MRAM material systems.