The Discovery of Giant Positive Magnetoresistance in Proximity to Helimagnetic Order in Manganese Phosphide Nanostructured Films

TL;DR

This paper reports the discovery of giant positive magnetoresistance near helimagnetic transition in nanostructured manganese phosphide films, enabled by confinement and strain effects, with potential applications in advanced magnetic sensors and spintronics.

Contribution

It introduces a novel strain-mediated spin helicity mechanism in nanostructured manganese phosphide, achieving unprecedented giant positive MR effects not seen in bulk materials.

Findings

Giant positive MR (90%) observed near FM-HM transition temperature in nanostructured films.

MR magnitude depends on grain size and temperature, with a peak at 110 K.

Strain and confinement effects induce a new spin helicity phenomenon in nanostructured helimagnets.

Abstract

The study of magnetoresistance (MR) phenomena has been pivotal in advancing magnetic sensors and spintronic devices. Helimagnets present an intriguing avenue for spintronics research. Theoretical predictions suggest that MR magnitude in the helimagnetic (HM) regime surpasses that in the ferromagnetic (FM) regime by over an order of magnitude. However, in metallic helimagnets like manganese phosphide, MR in the HM phase remains modest (10%), limiting its application in MR devices. Here, a groundbreaking approach is presented to achieve a giant low field MR effect in nanostructured manganese phosphide films by leveraging confinement and strain effects along with spin helicity. Unlike the modest MR observed in bulk manganese phosphide single crystals and large grain polycrystalline films, which exhibit a small negative MR in the FM region (2%) increasing to 8% in the HM region across 10-300 K, a grain size-dependent giant positive MR (90%) is discovered near FM to HM transition temperature (110 K), followed by a rapid decline to a negative MR below 55 K in manganese phosphide nanocrystalline films. These findings illuminate a novel strain-mediated spin helicity phenomenon in nanostructured helimagnets, presenting a promising pathway for the development of high-performance MR sensors and spintronic devices through the strategic utilization of confinement and strain effects.