Temperature evolution of nickel sulphide phases from thiourea complex and their exchange bias effect

• NiS2, NiS and Ni3S2 nanoparticles are obtained by thermal decomposition of nickel–thiourea complex at different temperatures.
• As the temperature is increased, nickel sulphide phase with lesser sulphur content is obtained.
• NiS2 nanoparticles show good exchange bias property which can be explained by antiferromagnetic core and ferromagnetic shell model.
• NiS2 and NiS are semiconducting while Ni3S2 shows metallic behavior.

Considering the very complex phase diagram of nickel sulphide, it is quite challenging to stabilize pure phases from a single precursor. Here, we obtain nanoparticles of various phases of nickel sulphide by decomposing nickel–thiourea complex at different temperatures. The first phase in the evolution is the one with the maximum sulphur content, namely, NiS2 nanoparticles obtained at 400 °C. As the temperature is increased, nanoparticles of phases with lesser sulphur content, NiS (600 °C) and Ni3S2 (800 °C) are formed. NiS2 nanoparticles exhibit weak ferromagnetic transition at 30 K and show a large exchange bias at 2 K. NiS nanoparticles are antiferromagnetic and show relatively smaller exchange bias effect. On the other hand, Ni3S2 nanoparticles exhibit very weak temperature dependent magnetization. Electrical measurements show that both NiS2 and NiS are semiconductors whereas Ni3S2 is a metal.

Pure phases of NiS2, NiS and Ni3S2 have been obtained by thermal decomposition of nickel–thiourea complex wherein, NiS2 nanoparticles exhibit remarkable exchange bias effect at 2 K.Figure optionsDownload as PowerPoint slide