Sign‐Tunable Magnetic Tunnel Junctions Engineered via Ferrimagnets for Efficient All‐Electrical and Thermal Switching

Abstract CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) have revolutionized modern spintronics, driving extensive efforts to optimize their properties such as spin polarization, perpendicular magnetic anisotropy, and switching speed. Here, a novel MTJ architecture is demonstrated, integrating ferrimagnetic CoTb to the conventional CoFeB/MgO/CoFeB MTJ structure, achieving both superior device performance and unique functionalities. The key innovation lies in the realization of sign‐tunable tunneling magnetoresistance (TMR), where the TMR ratio undergoes a dramatic transition from +33% (300 K) to ‐58% (30 K). This sign reversal, occurring at the ferrimagnetic compensation temperature ( T M = 212 K), stems from strong ferromagnetic (CoFeB‐Co sublattice) and antiferromagnetic (CoFeB‐Tb sublattice) couplings in the hybrid CoFeB/CoTb layers. Around T M , a distinctive spin‐flop mediated TMR sub‐loop is further observed at high field which provides additional resistance states. These resistance states can not only be switched by external magnetic field but also by thermal operations. Furthermore, energy‐efficient field‐free switching is demonstrated through synergistic spin‐orbit torque (SOT) and spin‐transfer torque (STT) effects, achieving all‐electrical switching of MTJ at J SOT = 5 MA cm −2 with a minimal 4.1% STT current incorporation. This innovative ferrimagnetic MTJ architecture establishes a new platform for developing next‐generation spintronic devices with superior functionality, operational versatility, and performance metrics.