Temperature-dependant phase transformation of NixFey?xOz nanoferrites: their dielectric and magnetic properties

Abstract

0–5 wt% nickel-doped iron oxide nanoparticles were synthesised using microwave-assisted method. Microwave-treated samples were annealed at 450 °C and 600 °C and named as Ni<inf>x</inf>Fe<inf>y?x</inf>O<inf>z</inf>-450 and Ni<inf>x</inf>Fe<inf>2?x</inf>O<inf>3</inf>-600 (x = 0. 0.1, 0.2, 0.3, 0.4 and 0.5), respectively. XRD, TGA, SEM and EDS were performed to study structural, thermal, morphological and compositional properties of the samples. Undoped sample has hematite phase at both 450 and 600°C, which is confirmed from both XRD and TGA. On nickel doping, an intermediate phase formed and there occurred two transition temperatures in TGA. Ni<inf>x</inf>Fe<inf>2?x</inf>O<inf>3</inf>-600 forms rhombohedral phase, while Ni<inf>x</inf>Fe<inf>y?x</inf>O<inf>z</inf>-450 forms a mixture of rhombohedral and inverse spinel structures till 2 wt% nickel concentration and pure inverse spinel structure above 2 wt% of nickel doping. M–H curves of samples from vibrating sample magnetometer (VSM) show the ferrimagnetic behaviour of both Ni<inf>x</inf>Fe<inf>y?x</inf>O<inf>z</inf>-450 and Ni<inf>x</inf>Fe<inf>2?x</inf>O<inf>3</inf>-600 except Fe<inf>2</inf>O<inf>3</inf>-600 which shows antiferromagnetic behaviour. In both set of samples, saturation magnetisation increases with increasing nickel concentration. Further, a two-probe method was used to study electrical and dielectric properties of the samples. AC conductivity (?<inf>ac</inf>), dielectric constant (??) and loss factor (tan ?) of Ni<inf>x</inf>Fe<inf>y?x</inf>O<inf>z</inf>-450 decreased with increase in 2 wt% nickel concentration and then increased with further increase in nickel, whereas these factors varied randomly with increasing nickel concentration for Ni<inf>x</inf>Fe<inf>2?x</inf>O<inf>3</inf>-600. ?<inf>ac</inf>, ?? and tan ? values of Ni<inf>x</inf>Fe<inf>2?x</inf>O<inf>3</inf>-600 are lower than those of Ni<inf>x</inf>Fe<inf>y?x</inf>O<inf>z</inf>-450, which can be attributed to the formation of hematite phase at 600 °C. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.