Field induced magnetic properties of Ni doped CoCr₂O₄

Ni doped CoCr₂O₄, (Co_1-xNi_x)Cr₂O₄ with x=0.5 and 0.25, nanoparticles were synthesized through sol-gel technique. The as synthesized samples were calcined at 600 °C for 1h. The phase identification of the samples was carried out using X-ray diffraction (XRD) techniques. The D_avg for (Co_0.5Ni_0.5)Cr₂O₄ and (Co_0.75Ni_0.25)Cr₂O₄ were found to be 33 (1) nm and 22 (1) nm, respectively, from the transmission electron microscopy (TEM). Magnetic properties of the nanoparticles were measured down to 2 K using a vibrating sample magnetometer (VSM). Magnetization as a function of temperature measured under 0.1, 0.5 and 1 T applied magnetic field show a hump like feature at the peak temperature, T_p, similar to the superparamagnetic blocking feature observed in many nanoparticle systems. With increasing applied magnetic field the T_p shifts towards lower temperature. Magnetization as a function of applied magnetic field (μ₀H= 0.1 T) showed an exchange bias like feature for x= 0.5, whereas no shifting of the loop was observed for x=0.25 sample. The transition related to spiral ordering at temperature T_S was observed for both the samples, whereas no lock-in transition at temperature T_L was noticed.