3D domain wall motion memory with artificial ferromagnet

Racetrack memory using domain wall (DW) motion in ferromagnetic nanowires is a potential candidate for future memory technologies. However, there are still problems that hamper the commercialization. First, lowering consumption power is crucial for practical application. Second, a precise control of DW position is a problem to be solved. Smaller DW width is preferable for higher density memory. Here, we propose a new type of 3D DW motion memory with an artificial ferromagnet and study its feasibility by micromagnetic simulation. 

3D DW motion memory proposed in this study consists of an array of cylindrical artificial ferromagnetic wires, which is composed of periodically stacked bilayers of a bit layer with strong magnetic anisotropy and a DW layer with no magnetic anisotropy. The data is written by flipping the magnetization of the bottom bit layer using the spin-orbit torque induced by the current in the word line. The written data can be shifted to the arbitrary position in the artificial magnetic wire by the appropriate current injection through the wire. By repeating the writing and shifting, an arbitrary information sequence can be stored in the magnetic wire. The data can be read out with the topmost magnetic tunnel junction while the data is being shifted by the current through the wire. Micromagnetic simulation shows that the precise DW position controllability, narrow DW width down to 3 nm, and low DW motion current down to 2 × 1010 A/m2 can be achieved with feasible material parameters. Furthermore, it is found that the high thermal stability and the low DW motion current can be achieved simultaneously. Data-writing and shifting processes for 2-bits memory have been demonstrated. Although the originally proposed method for reading information from this device is destructive, we proposed a novel nondestructive readout method, leveraging the magnetization dynamics induced by the spin transfer torque. This work was partly supported by JST, CREST (Grant Number JP MJCR21C1), Japan.

Séminaire organisé dans le cadre du programme interdisciplinaire MAT-PULSE (Materials and Physics @ Ultimate Scale: Nanotech for a sustainable digital world)