A study of crossover from 3D ferrimagnetic bulk NiCrO compound into 2D spin-glass-like nanophase.

In this report, the magnetic behaviour of bulk and nanoparticles of NiCrO under different applied magnetic fields has been investigated extensively. Nanoparticles of NiCrO (12 nm) were obtained by mechanical milling of polycrystalline powder prepared by polyol method. FC-ZFC measurement of bulk at different applied magnetic fields has revealed the existence of a ferrimagnetic transition around 66 K followed by an antiferromagnetic transition close to 30 K. However, its nano counterpart has shown remarkable change in magnetic properties-a suppression of ferrimagnetic transition accompanied by strengthening low-temperature magnetic phase and observation of a new transition at 90 K ( T), which is weakly magnetic in nature. The frequency-dependent ac susceptibility data of nanoparticles have been fitted to the well-known de Almeida-Thouless equation and a H dependence of the low-temperature peak is observed with a resulting zero-field freezing temperature ( T) equal to 10.1 K. Further, the dynamical behaviour near freezing temperature has been analysed in terms of critical behaviour and the obtained fitted parameter values were found to be τ (relaxation time constant) = 3.6 × 10 s, T = 8.7 K and zν = 11.1. Moreover, Vogel-Fulcher law has been used to understand the nature of freezing transition, and the parameters after fitting are obtained as E/ k = 58.9 K, τ = 5.22 × 10 s and T = 8.03 K. Finally, the spin-glass phase is concluded. Moreover, in contrast to bulk, the H dependence of freezing temperature of nanoparticles sample (75 h) does support the 2D surface-like spin-glass nature. [ABSTRACT FROM AUTHOR]