High-temperature solvothermal synthesis and magnetic properties of nearly monodisperse CdCr₂S₄ nanocrystals

Magnetic spinel CdCr₂S₄ nanocrystals have been synthesized using a high-temperature solvothermal method. The synthesis process involves the reaction of excess 1-dodecanethiol (1-DDT) with CdCl₂ and CrCl₃·6H₂O in 1-octadecene (ODE) solution carried out in a sealed titanium alloy autoclave. Nearly monodisperse spherical CdCr₂S₄ nanocrystals with an average size of 8.0 ± 1.5 nm are obtained. X-ray diffraction patterns confirm formation of the pure spinel phase without any impurities. Magnetic measurements indicate a Curie temperature (T_c) of ∼76 K for the synthesized CdCr₂S₄ nanocrystals, which are ferromagnetic at lower temperatures with a saturation magnetization value of 19 emu g^-1 at 5 K. The magnetic entropy change ΔS_m, evaluated from isothermal magnetic measurements, exhibits a maximum around 82 K, with a value of -ΔS_m = 0.86 J kg^-1 K^-1 at H_max = 5 T. ΔS_m spans a broad temperature range, with a full width at half maximum of ∼88 K in the magnetic field range of 0-5 T, which is attractive for magnetic refrigeration applications in the liquid nitrogen temperature range.