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

• Pure CoCr2 − xFexO4 (x = 0.1 and 0.2) nanoparticles of 16–20 and 6–10 nm show enhancement of Tc from 100 to 110 K and Ts from 18 K to 36 K with increasing Fe.
• The theoretical variation of reciprocal susceptibility with temperature in paramagnetic region using the function χ−1 = T/C + 1/χ0 – b/(T − θ) is fitted with the experimental data.
• The difference in ferrimagnetic Curie point, θf and paramagnetic Curie point, θp is 30 K and 7 K respectively for sample x = 0.1 and 0.2 indicating a sharp ferri- to para-magnetic transition in the former one.

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.

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