Magnetic Properties and Crystalline Transition for the NiCr_1.7Fe_0.3O₄

We have studied the temperature dependent magnetic properties and crystalline phase transitionn in small amount Fe doped nickel chromite. The Crystalline structure of $NiCr_1.7Fe_0.3O_4$ is spinel cubic (Fd-3m) structure with a lattice constant $a_0=8.317\AA$ at room temperature. The magnetic $N\acute{e}el$ temperature $(T_N)$ of the Fe doped nickel chromite sample is determined to be 250 K. The $M\ddot{o}ssbauer$ spectra exhibit that there are two magnetic phases with the two different sites for the $Cr³⁺$ ions. The spectrum at 4.2 K is fitted to two magnetic components of the magnetic hyperfine fields $H_hf=496$ and 485 kOe. From the spectrum at 295 K, the electric quadrupole splittings are observed with large values of 0.49 and 0.50 mm/s, respectively. The values of the isomer shifts at all temperature ranges show that the Fe ions are ferric states. We are suggested that the dynamic Jahn-Teller distortion and anisotropic magnetic relaxation effects due to the crystalline phase transition.