Perpendicular magnetic tunnel junctions in the broader spintronics landscape: a comprehensive review of spin transfer torque, voltage-controlled magnetic anisotropy, spin-orbit torque, and optical control

Abstract Magnetic tunnel junctions (MTJs) have emerged as a cornerstone of next-generation spintronic memory and computing, yet no single control paradigm offers a universal solution across all performance dimensions. This review provides a comprehensive survey of MTJ switching mechanisms, from established perpendicular spin-transfer torque (p-STT) to voltage-controlled magnetic anisotropy (VCMA), spin-orbit torque (SOT), all-optical control, and hybrid combinations thereof.We begin with p-STT MTJs, examining their materials physics, simulation frameworks, and integration maturity, while critically addressing persistent limitations including write-current endurance, read disturb, stochastic switching, and scalability constraints below 20nm. We then turn to VCMA-based devices, where interfacial engineering in CoFeB/MgO heterostructures enables sub-volt, ultralow-power operation. SOT architectures follow, leveraging the spin Hall effect in heavy-metal/ferromagnet bilayers to achieve sub-nanosecond, three-terminal switching . We subsequently survey emerging all-optical control strategies, including the inverse Faraday effect and plasmon-enhanced photothermal switching in ferrimagnetic heterostructures, unlocking picosecond and potentially terahertz-rate operation. Finally, hybrid schemes including STT+VCMA, STT+SOT, voltage gated SOT, and optically-assisted electrical switching are examined, revealing synergistic pathways to overcome the individual bottlenecks of each mechanism. For each paradigm, key physical effects, material strategies, performance metrics, applications, and remaining challenges are discussed.