Evidence of cluster glass phase, exchange bias, reversible magnetocaloric effect and study of electrical properties in Ni${}_{1-x}$Cd${}_x$Cr${}_2$O${}_4$ (x = 0-0.30) spinel

Effect of cadmium (Cd) substitution on magnetic and electrical properties of spinel Ni${}_{1-x}$Cd${}_x$Cr${}_2$O${}_4$ (x = 0-0.30) samples have been studied. Due to non-Jahn-Teller Cd ion substitution, a structural transition from the tetragonal (I4${}_1$/amd) to cubic (Fd$\overline{3}$m) phase is seen at room temperature. The long-range competitive ferrimagnetic and antiferromagnetic interactions in the x = 0.05 and 0.10 samples are responsible for the observed large value of coercive and exchange bias field. Cd substitution significantly enhances the antiferromagnetic component of canted spin structure of NiCr${}_2$O${}_4$ and leads to a cluster glass phase for x = 0.30 samples. Observed memory effect and relaxation of isothermal remanent magnetization confirms the metastability and nonequilibrium dynamics in the glassy phase. For x = 0.20 sample, we have observed reversible magnetocaloric behavior with a maximum negative entropy change of -ΔS${}_M$= -1.031(3) × 10${}^{-4}$ cal/gK. Dielectric, impedance and ac conductivity data have been investigated in the temperature range of T = 27-300 K and frequency range of f = 20-10${}^5$ Hz. Study of impedance spectra and ac conductivity indicates non Debye type of dielectric relaxation and correlated barrier hopping (CBH) of charge carriers is controlling the conduction mechanism in these samples.