Controlled growth of Ni/NiO composite nanoparticles and its influence on exchange anisotropy and spin glass features

Abstract

The current study focus on the exchange bias properties of Ni/NiO ferromagnetic-antiferromagnetic nanocomposite by fabricating Ni (FM) using a one-step solution combustion method. The prepared Ni nanoparticles were oxidized at 400 °C for different time durations (τ = 3, 6, 12, 24, 48, 72, 96, 120, 144 and 168 h) in the ambient atmosphere to grow NiO (AFM). The X-ray diffraction pattern of the Ni/NiO nanocomposite indicate good crystallinity of the samples. Raman spectroscopy exhibited a short-range magnon excitation around 1400 cm−1 that indicate the contribution of AFM exchange energy between the Ni2+-O2--Ni2+ chain in the composites. The presence of Ni and NiO phases were confirmed by room temperature magnetization measurement. For the better understanding of the exchange bias of the Ni/NiO nanocomposite subjected to heat treatment for several hours (0–168 h), zero-field cooled and field cooled M-H and M-T measurements were made. The hysteresis loop shift along the field axis and enhanced coercivity values shows the exchange bias effect in the Ni/NiO structure in the controlled oxidation process. The Ni and NiO interfacial effect and phase fraction have significant effect on the observed exchange bias. Moreover, finite size effects contribution on the antiferromagnetic exchange and spin glass features observed at a temperature of 24 K of the Ni/NiO system contribute to the large exchange bias and enhanced coercivity.