Low temperature magnetic study of α-NiS nanoparticles synthesized via hydrothermal technique

Abstract

Synthesis of material with nano-order anisotropy has always been a tricky task for the researchers, since there has to be some property-based inhomogeneity present within the homogeneous material. In this report, we discuss the emergence of Exchange Bias (EB), which is itself a case of magnetic property based anisotropy. Here, a thorough low temperature magnetic study of nickel sulfide (NiS) nanoparticles synthesized via solution based hydrothermal technique was performed. To introduce nano-order inhomogeneity we played with different feeding flow rate of the starting materials. The synthesized samples were of highly crystalline mixed phase nature with α-NiS as a dominant phase. Variation in energy bandgap as a function of feeding rate suggests the possibility of the formation different-sized seed cluster. For sample with maximum α-NiS content, presence of strong magnetic coupling at T<Tbarising from uncompensated spins at the surface of the nanoparticles suggest its weak ferromagnetic character with a paramagnetic background. For the first time, an unusual phenomenon of exchange bias (EB) was also observed for the sample with maximum α-NiS content. The presence of EB suggests FM-AFM coupling occurring over the particle surface, which is also prudent from the fact that NiS is intrinsically an antiferromagnetic material. In short the present study opens up the possibility for the use of NiS a possible material spin based device applications. © 2021 Elsevier Ltd. All rights reserved.