Shilei Zhang

Abstract:

Stacking nonvolatile memory cells into a three-dimensional matrix represents a powerful solution for the future of magnetic memory. However, it is technologically challenging to access the data in the storage medium if large numbers of bits are stacked on top of each other. Here we introduce a new type of multilevel, nonvolatile magnetic memory concept, the magnetic abacus. Instead of storing information in individual magnetic layers, thereby having to read out each magnetic layer separately, the magnetic abacus adopts a new encoding scheme. It is inspired by the idea of second quantisation, dealing with the memory state of the entire stack simultaneously. Direct read operations are implemented by measuring the artificially engineered ‘quantised’ Hall voltage, each representing a count of the spin-up and spin-down layers in the stack. This new memory system further allows for both flexible scaling of the system and fast communication among cells. The magnetic abacus provides a promising approach for future nonvolatile 3D magnetic random access memory.

Abstract:

A large enhancement of anomalous Hall sensitivity (Sv) by metal/oxide interfacial modification is obtained in a MgO/[Co/Pt]3/MgO multilayered structure. The values of Sv are increased to 8363 V/A·T by CoO insertion and 2261 V/A·T by Pt insertion, while Sv is approximately 1000 V/A·T in normal Hall semiconductor sensors. Microstructural analysis shows that the crystal orientation of [Co/Pt]3 multilayers is improved, and the oxygen concentration is largely changed by introducing an ultrathin CoO layer at metal/oxide interfaces, leading to a large increment of Sv.

Abstract:

Multivalued logic devices are promising candidates for achieving high-density, low-power memory and logic functionalities. We present a ferromagnetic multilayer Hall junction device with four distinct resistance - and thus logic - states. The states can be encoded as a quaternary bit and decoded into two binary bits. We demonstrate a nonvolatile full adder that is based on a single Hall junction, the extraordinary Hall balance. The device can be easily integrated into complex logic circuits for logic-in-memory architectures.