A perspective on electrical generation of spin current for magnetic random access memories

Abstract

Spin currents are used to write information in magnetic random access memory (MRAM) devices by switching the magnetization direction of one of the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) nanopillar. Different physical mechanisms of conversion of charge current to spin current can be used in two-terminal and three-terminal device geometries. In two-terminal devices, charge-to-spin conversion occurs by spin filtering in the MTJ's ferromagnetic electrodes and present day MRAM devices operate near the theoretically expected maximum charge-to-spin conversion efficiency. In three-terminal devices, spin–orbit interactions in a channel material can also be used to generate large spin currents. In this Perspective article, we discuss charge-to-spin conversion processes that can satisfy the requirements of MRAM technology. We emphasize the need to develop channel materials with larger charge-to-spin conversion efficiency—that can equal or exceed that produced by spin filtering—and spin currents with a spin polarization component perpendicular to the channel interface. This would enable high-performance devices based on sub-20 nm diameter perpendicularly magnetized MTJ nanopillars without need of a symmetry breaking field. We also discuss MRAM characteristics essential for CMOS integration. Finally, we identify critical research needs for charge-to-spin conversion measurements and metrics that can be used to optimize device channel materials and interface properties prior to full MTJ nanopillar device fabrication and characterization.

Anomalous Hall Effect in Epitaxial Thin Films of the Hexagonal Heusler MnPtGa Noncollinear Hard Magnet

“…We foresee that Heusler and half-Heusler compounds, with noncollinear magnetic groundstates, [28,43,[45][46][47][48][49][50] should exhibit rich transport properties endowed by their Berry curvature, whose various manifestations remain partially unexplored and origin(s) in part unexplained. Beyond the celebrated electrodynamics of magnetic skyrmion quasi-particles, [51] Heusler compounds offer a rich platform for the exploration of their prospective use in functional spintronics devices with PMA (e.g., for SO-torque-induced switching of magnetic random access memory devices [52,53] ), with the additional motivation of establishing new transport signatures [54,55] and overall new understandings of noncollinear magnetic structures.…”

Nonvolatile Memristive Materials and Physical Modeling for In‐Memory and In‐Sensor Computing

“…To modulate the magnetic state of the free layer, the MTM layer based on the STT effect utilizes the spin‐polarization phenomenon. [ 220 ] Most electrons become spin polarized by the magnetization direction of the fixed layer if the electrons pass through the magnetically fixed layer. [ 221 ] The electrons then render the spin‐angular momentum to the free magnetic layer, thus altering the magnetization direction of the free layer to that of the fixed layer, viz., the parallel mode results (Figure 5a).…”

Probing the structural, magneto-electronic, thermophysical, and thermoelectric properties of vanadium-based V2MnZ (Z = As, Ga) Heusler alloy: a computational assessment

“…Vanadium-based full Heusler alloys [9] possess half-metallic ferromagnets (HMFs) behavior, while half-Heusler alloys behave differently. The discovery of new materials with half-metallic behavior and 100% spin polarization has led to their use in spin injectors for magnetic random-access memories and other spin-dependent devices [10].…”