Dynamic Characterization of Spintronic Devices: MTJ high-bias write errors, and spin-orbit torque from the planar Hall effect

Abstract

Magnetic tunnel junctions (MTJ) are a promising candidate for non-volatile memory applications. In these devices, information is stored in the relative orientation between two ferromagnetic layers, separated by an insulating barrier. One layer, called a “free” layer, is switchable by exerting a spin torque from a spin polarized charge current. In principle, the switching speed increases as the amount of spin current is increased. However, at higher write currents, an increase in write-errors is often seen contrary to this expectation. We investigate the mechanism for these errors using frequency and time domain electrical measurements, in comparison to macrospin numerical simulations. We find that the formation of undesirable dynamic states between the ferromagnetic layers and interfacial layers can explain the experimental observations. Understanding of write-error mechanisms is of importance since it ultimately limits the device performance. One potential way the solve this dynamics issue, is to separate the read and write paths of the MTJ. For perpendicular MTJ, this requires a method to convert an in-plane charge current into a perpendicularly flowing spin current with an out-of-plane polarization. We also describe efforts to realize such spin currents experimentally using the planar Hall effect, found in ferromagnetic materials. We find that a partially out of plane polarized spin current can be produced. The strength of this effect is comparable to the spin Hall effect, indicating that the planar Hall effect may be a potential source of spin current.