Synthesis Condition Reflected Structural and Magnetic Properties Of Li_(0.5)Cr_(0.5)Fe_2O_4 Nanoparticles

摘要

Morphological and magnetic characteristics of lithium-chromate ferrite (Li_(0.5)Cr_(0.5)Fe_2O_4) nanoparticles synthesized by sol-gel auto combustion method using nitrates of respective metal ions have been studied. Synthesized powders were annealed at four different temperatures viz. 600 ℃, 800 ℃, 1000 ℃ and 1200 ℃. The sample annealed at 600 ℃ was also treated for four different annealing time viz. 4 h, 8 h, 12 h and 16 h. The ferritization temperature was determined by TG/DTA. The structure and the crystal phase of the powder were characterized on an X-ray diffractometer (XRD). The XRD patterns revealed that all the products consisted of nanocrystalline ferrite phase only. The shape and the size were analyzed by transmission electron microscope (TEM). The TEM observations showed that majority of the particles are spherical in shape, fairy monodispersed and the size varied in the range of 12-50 nm. The size of the nanoparticles increases linearly with increase in annealing temperature and time. Cation distribution obtained from XRD shows that freshly prepared particles are in a metastable state with regard to the cation distribution between the A and B sites of the spinel lattice whereas heat treated samples are in stable state. The infrared spectra showed two dominant bands in the high- and low-frequency range which are assigned to the tetrahedral and octahedral complexes, respectively. Magnetic ordering was evaluated by characterizing the samples by vibrating sample magnetometer (VSM) and zero field cooled (ZFC). Typical blocking effects are observed below about 233 K. Blocking temperature increases with increasing annealing temperature and annealing time. Dielectric constant increases with increasing annealing temperature.