Electrical conductivity and magnetic field dependent current-voltage characteristics of nanocrystalline nickel ferrite

We have studied the grain size dependent electrical conductivity, dielectric relaxation and magnetic field dependent current voltage (I-V) characteristics of nickel ferrite (NiFe2O4). The material has been synthesized by sol-gel self-combustion technique, followed by ball milling at room temperature in air environment to control the grain size. The material has been characterized using X-ray diffraction (refined with MAUD software analysis) and Transmission electron microscopy. Impedance spectroscopy and /V characteristics in the presence of variable magnetic fields have confirmed the increase of resistivity for the fine powdered samples (grain size 5.17 +/- 0.6 nm), resulted from ball milling of the chemical routed sample. Activation energy of the material for electrical charge hopping process has increased with the decrease of grain size by mechanical milling of chemical routed sample. The I V curves showed many highly non-linear and irreversible electrical features, e.g., I V loop and bi-stable electronic states (low resistance state-LRS and high resistance state-HRS) on cycling the electrical bias voltage direction during I-V curve measurement. The electrical dc resistance for the chemically routed (without milled) sample in HRS (similar to 3.4876x10(4) Omega) at 20 V in presence of magnetic field 10 kOe has enhanced to similar to 3.4152x10(5) Omega for the 10 h milled sample. The samples exhibited an unusual negative differential resistance (NDR) effect that gradually decreased on decreasing the grain size of the material. The magneto-resistance of the samples at room temperature has been found substantially large (similar to 25-65%). The control of electrical charge transport properties under magnetic field, as observed in the present ferrimagnetic material, indicate the magneto-electric coupling in the materials and the results could be useful in spintronics applications.