Large zero-field Hall & Nernst effects and AMR in aligned MnBi / Bi composites

The Hall and Nernst effects involve the detection of a transverse voltage due to the effect of the Lorentz force on the flow of electrons under an applied electric field or temperature gradient. In ferromagnets, the application of a magnetic field affects the transverse resistivity- the anisotropic magnetoresistance (AMR). Typically, these require an external applied magnetic field to produce a detectable transverse signal. However, here we show that bulk composites of magnetically aligned, unidirectional MnBi needle-like inclusions inside a Bi matrix produce a robust and large Hall, Nernst, and AMR voltage at zero field. The strong spin-orbit coupling in Bi and the large magnetic moment provided by MnBi combine in this composite to give extraordinary AMR ratios. Their zero-field effects come on top of the large in-field Nernst and spin-Seebeck effects reported previously [1]. This material opens new device prospects for magnetic sensing, microwave propagation, and information filtering.
[1] Nanomaterials 2020, 10(10), 2083; DOI: 10.3390/nano10102083