Magnetic ratchet for three-dimensional spintronic memory and logic

Abstract

One of the key challenges for future electronic memory and logic devices is finding viable ways of moving from today's two-dimensional structures, which hold data in an x-y mesh of cells, to three-dimensional structures in which data are stored in an x-y-z lattice of cells. This could allow a many-fold increase in performance. A suggested solution is the shift register--a digital building block that passes data from cell to cell along a chain. In conventional digital microelectronics, two-dimensional shift registers are routinely constructed from a number of connected transistors. However, for three-dimensional devices the added process complexity and space needed for such transistors would largely cancel out the benefits of moving into the third dimension. 'Physical' shift registers, in which an intrinsic physical phenomenon is used to move data near-atomic distances, without requiring conventional transistors, are therefore much preferred. Here we demonstrate a way of implementing a spintronic unidirectional vertical shift register between perpendicularly magnetized ferromagnets of subnanometre thickness, similar to the layers used in non-volatile magnetic random-access memory. By carefully controlling the thickness of each magnetic layer and the exchange coupling between the layers, we form a ratchet that allows information in the form of a sharp magnetic kink soliton to be unidirectionally pumped (or 'shifted') from one magnetic layer to another. This simple and efficient shift-register concept suggests a route to the creation of three-dimensional microchips for memory and logic applications.

Spin‐Structured Multilayers: A New Class of Materials for Precision Spintronics

“…This includes GMR and TMR spin valves [ 35 ] for magnetic sensors, magnetoresistive random access memory (MRAM) cells and a multitude of systems that are based on spin-transfer torque. The large parameter range of coercivities and easy axes orientations possible in one single device will lead to qualitative advances, e.g., new types of 3D multilevel magnetic memory cells [ 36,37 ] and the design of switchable ferromagnetic/nonmagnetic hybrid structures (e.g., ferromagnet/superconductor hybrids [ 38 ] ).…”

A robust soliton ratchet using combined antiferromagnetic and ferromagnetic interlayer couplings

“…1,14,15 We have previously demonstrated a vertical ratchet scheme which uses entirely antiferromagnetic coupling between perpendicularly magnetized layers, using alternating layer thickness and interlayer coupling strengths. 1,16 In this paper, we demonstrate that a repeated sequence of antiferromagneticantiferromagnetic-ferromagnetic (AF-AF-F) coupled magnetic layers creates a synchronous vertical soliton ratchet whilst using layers of the same material and thickness. We show theoretically how this scheme can support solitons across both antiferromagnetically and ferromagnetically coupled layers creating a generalized ratchet scheme.…”

“…[1][2][3] One way to create a data bit in such devices is through an elementary excitation from the ordered ground state. This can be considered to be a domain wall, separating regions with opposite magnetism in the simplest case, or dividing the two energetically degenerated states in antiferromagnetically coupled lattices.…”

“…Second, it is possible for layer d to switch at the same time as c. This gives two step propagation and is equivalent to the ratchet using varying thickness layer previously demonstrated. 1 The switching fields assuming a soliton across J FM are…”

“…[2][3][4][5][6][7][8] This form of domain wall, which can occur in both continuous and discontinuous systems, is a magnetic kink soliton, which is referred to as a soliton in this work. 1,6,9 Two main classes of magnetic materials can be used, shape anisotropy dominated and perpendicularly magnetized. For shape dominated materials, a chirality of rotation can be defined in the wall separating the two states.…”