The spin torque memristor is based on a
with a magnetic domain wall in its free layer.
The trilayer resistance depends on the relative proportion of parallel and anti-parallel domains, which is set by the domain wall
position. The more the domain wall is to the left, the closer the configuration is to the parallel state, the smaller the
resistance. Using the
effect, it is possible to manipulate the position of a magnetic DW. The domain wall displacement
Δx then depends on the amplitude j of the injected current as well as the pulse duration Δt: Δx = j.Δt = Δq.
Therefore the resistance depends on the charge, and a spin torque memristor is obtained. The classical way to move a DW by spin
transfer is to inject the current laterally. If the trilayer is a metallic spin-valve, the same lateral geometry allows reading the
device resistance, thanks to Current-In-Plane (CIP) magneto-resistance.
have proposed to use this geometry to implement the
spin torque memristor. Unfortunately, the CIP magnetoresistance ratios in spin-valves are limited to a few %, which would give rise to
OFF/ON ratios well below 1. This is much too low for discriminating the different states in a real-world application, and even
more for implementing these devices in crossbar arrays.
The solution to increase the OFF/ON ratio up to 6 and more is to use magnetic tunnel junctions.
In that case reading can only be achieved by applying the probe current vertically across the junction. The spin torque memristor
concept that we propose is based on vertical writing as well. This has two advantages. First, since the reading and writing paths
are the same, we keep a two-terminal, easy to scale down, conform to definition memristor. Secondly, as we have shown,
spin torque induced domain
wall motion by vertical injection is much more efficient than the lateral scheme.