Annular Spin-Transfer Memory Element

TL;DR

This paper proposes an annular magnetic memory device utilizing spin-polarized currents to switch magnetization states, offering advantages in stability, ease of switching, and separate read/write operations compared to traditional MRAM.

Contribution

Introduction of an annular spin-transfer memory element with separate read/write contacts, enhancing stability and operational efficiency over conventional spin-transfer MRAM.

Findings

Stable magnetization states in ring geometry

Efficient switching with short current pulses

Separate read/write contacts improve performance

Abstract

An annular magnetic memory that uses a spin-polarized current to switch the magnetization direction or helicity of a magnetic region is proposed. The device has magnetic materials in the shape of a ring (1 to 5 nm in thickness, 20 to 250 nm in mean radius and 8 to 100 nm in width), comprising a reference magnetic layer with a fixed magnetic helicity and a free magnetic layer with a changeable magnetic helicity. These are separated by a thin non-magnetic layer. Information is written using a current flowing perpendicular to the layers, inducing a spin-transfer torque that alters the magnetic state of the free layer. The resistance, which depends on the magnetic state of the device, is used to read out the stored information. This device offers several important advantages compared to conventional spin-transfer magnetic random access memory (MRAM) devices. First, the ring geometry offers stable magnetization states, which are, nonetheless, easily altered with short current pulses. Second, the ring geometry naturally solves a major challenge of spin-transfer devices: writing requires relatively high currents and a low impedance circuit, whereas readout demands a larger impedance and magnetoresistance. The annular device accommodates these conflicting requirements by performing reading and writing operations at separate read and write contacts placed at different locations on the ring.