Non-reciprocal magnetoresistance, directional inhomogeneity and mixed symmetry Hall devices

TL;DR

This paper demonstrates nonreciprocal magnetoresistance effects in ferromagnetic films with engineered inhomogeneity, leading to enhanced antisymmetric Hall signals and multi-bit memory capabilities for spintronics applications.

Contribution

It introduces a novel approach using engineered inhomogeneity to achieve nonreciprocal transport and mixed symmetry Hall devices, surpassing previous unidirectional magnetoresistance effects.

Findings

Antisymmetric Hall signals are 10-1000 times larger than in unidirectional magnetoresistance.

Multi-bit memory is realized in partitioned ferromagnetic-normal metal structures.

Engineered inhomogeneity enables nonreciprocal transport phenomena in ferromagnetic films.

Abstract

Phenomenology similar to the nonreciprocal charge transport violating Onsagers reciprocity relations can develop in directionally inhomogeneous conducting films with nonuniform Hall coefficient along the current trajectory. The effect is demonstrated in ferromagnetic CoPd films and analyzed in comparison with the unidirectional magnetoresistance phenomena. We suggest to use an engineered inhomogeneity for spintronics applications and present the concept of mixed symmetry Hall devices in which transverse to current Hall signal is measured in a longitudinal contacts arrangement. Magnetization reversal and memory detection is demonstrated in the three terminal and the partitioned normal metal-ferromagnet (NM - FM) device designs. Multi-bit memory is realized in the partitioned FM-NM-FM structure. The relative amplitude of the antisymmetric signal in the engineered ferromagnetic devices is few percent which is 10 to 1000 times higher than in their unidirectional magnetoresistance analogues.