Cobalt chromite obtained by thermal decomposition of oxalate coordination compounds

Cobalt chromites (CoCr2O4) powders have been synthesized via thermal decomposition of oxalate precursor compounds (NH4)4[CoCr2(C2O4)4(OH)4]·7H2O (I) and (NH4)12[CoCr2(C2O4)8(OH)4]·(NH4)2C2O4·12H2O (II). The oxalate precursors have been characterized by infrared (IR) and ultraviolet–visible spectroscopy (UV–vis), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis. The structure, morphology and magnetic properties of CoCr2O4 powders have been investigated by XRD, SEM, IR and Raman spectroscopy (RS), UV–vis and magnetic measurements. XRD patterns confirmed the formation of spinel-type cobalt chromite, with average crystallite sizes calculated from XRD patterns of 38 nm and 58 nm, for spinel chromites from precursors I and II, respectively. SEM micrographs revealed particle sizes between 30 and 130 nm, with a low degree of aggregation of primary nanocrystallites. Both CoCr2O4 powders presented ferrimagnetic ordering below the Currie temperature (Tc) and a phase transition at Ts~20 K attributed to the onset of long-range spiral magnetic order.