Abstract
Spinel nanocrystals of Cd1−xCoxCr2O4 (0 ≤ x ≤ 1) solid solution are successfully synthesized by a microwave combustion method and their properties are systematically studied. Single phase spinel structure is determined for all the synthesized compositions by x-ray diffraction (XRD) and the two vibrational bands of metal-oxide bonds are assigned by Fourier transform infrared spectroscopy (FTIR). Energy dispersive x-ray spectroscopy (EDX) indicates almost stoichiometric compositions in the whole range of x of the synthesized Cd1−xCoxCr2O4 nanoparticles. Crystallite sizes of 6 – 10 nm estimated from XRD patterns are in consistence with sizes of cubic nanocrystals observed by transmission electron microscopy (TEM). The lattice constant behavior with x shows a deviation from Vegard’s law with a kink anomaly at x ∼ 0.5 that may be attributed to different site-preferences of divalent cations in the two spinel sublattices. Optical absorbance measurements reveal a wide energy gap of 3.5 eV for CdCr2O4 nanoparticles that is smoothly narrowed by Co-substitution for Cd to become 3 eV in pure CoCr2O4 with particular optical characteristics. Magnetization isotherms measured at 300 K confirm the parmagnetic behavior, while those measured at 2 K show hysteresis evolution from a suppressed antiferromagnetic state to a ferrimagnetic state with maximum coercivity for Cd0.7Co0.3Cr2O4.
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