Intrinsic giant magnetoresistance due to exchange-bias-type effects at the surface of single-crystalline NiS₂ nanoflakes

The coexistence of different properties in the same material often results in exciting physical effects. At low temperatures, the pyrite transition-metal disulphide NiS₂ hosts both antiferromagnetic and weak ferromagnetic orders, along with surface metallicity dominating its electronic transport. The interplay between such a complex magnetic structure and surface-dominated conduction in NiS₂, however, is still not understood. A possible reason for this limited understanding is that NiS₂ has been available primarily in bulk single-crystal form, which makes it difficult to perform studies combining magnetometry and transport measurements with high spatial resolution. Here, NiS₂ nanoflakes are produced via mechanical cleaving and exfoliation of NiS₂ single crystals and their properties are studied on a local (micron-size) scale. Strongly field-asymmetric magnetotransport features are found at low temperatures, which resemble those of more complex magnetic thin film heterostructures. Using nitrogen vacancy magnetometry, these magnetotransport features are related to exchange-bias-type effects between ferromagnetic and antiferromagnetic regions forming near step edges at the nanoflake surface. Nanoflakes with bigger steps exhibit giant magnetoresistance, which suggests a strong influence of magnetic spin textures at the NiS₂ surface on its electronic transport. These findings pave the way for the application of NiS₂ nanoflakes in van der Waals heterostructures for low-temperature spintronics and superconducting spintronics.