Studies of magnetic behavior of chemically synthesized interacting superparamagnetic copper ferrite nanoparticles

The magnetic property of nanocrystalline copper ferrite (CuFe 2 O 4 , CF) with narrow size distribution synthesized by co-precipitation technique is investigated. The occupancy of cations among the tetrahedral and octahedral sites is determined from the Rietveld analysis of the X-ray diffraction (XRD) pattern. Microstructural, optical, and magnetic properties of the ferrite nanoparticles (NPs) are analyzed in detail using high-resolution transmission electron microscopy (HRTEM), UV–Vis absorption spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and superconducting quantum interference device (SQUID) magnetometer. The blue shift in optical band gap compared to bulk one is observed due to the smaller particle size. The particle size distribution inferred by mathematical analysis from the variation of difference between field cooled (FC) and zero field cooled (ZFC) magnetization with temperature supports the HRTEM observation. M–T curve initially proposes the presence of superparamagnetic (SPM) NPs with non-interacting core and interacting surface spin. Therefore magnetic behavior of the sample is explained by core–shell model. This fact is substantiated from the good fitting of M–H curves at different temperatures using a combined equation generated from ‘Law of approach’ to saturation magnetization and Langevin function. With the lowering of temperature magnetic blocking and random spin freezing process occurs. The ratio of M_R /M_s (remanent/saturation magnetization) less than 0.5 for all temperatures implies the presence of uniaxial anisotropy of the single-domain NPs. The unsaturated nature of the M–H curves may be due to the combined contribution from SPM core and spin canting in the mixed spinel CuFe 2 O 4 .