Tuning of magnetic transition temperatures in nanoparticles of CoCr2O4 multiferroic by B-site mixing

Pure CoCr2 − xFexO4 nanoparticles synthesized through conventional coprecipitation technique show particle size distribution in the range of 16–20 and 6–10 nm for x = 0.1 and 0.2 respectively. Magnetic and specific heat measurements show an enhancement of paramagnetic to collinear ferrimagnetic transition temperature, Tc from 100 to 110 K and to a short range non-collinear spiral ordering, Ts from 18 to 36 K with increasing x from 0.1 to 0.2 respectively. In addition, a strong disagreement between the paramagnetic moment obtained from the fitting of χ−1 = T/C + 1/χ0 – b/(T − θ) and ferrimagnetic moment measured from the M vs. H loop at 10 K corroborates the nonsaturation behavior of magnetization at 50–100 kOe field and an order of magnitude higher coercivity (Hc). The enhancement of Tc and Ts with increasing Fe concentration is attributed to an intrinsic change in non-collinear to collinear spin structure and strong JA–B interaction.