Role of surface defects and anisotropy variation on magnetic properties of copper ferrite nanoparticles prepared by co-precipitation method

Nanocrystalline Cu-ferrite samples were synthesized by co-precipitation method at two different pH. The samples were annealed at various temperatures ranging from 400 to 1000 °C in air for 3 h. Tetragonal Cu-ferrite was observed for the sample prepared at pH = 10.9, whereas the sample prepared at pH = 10.3 showed cubic Cu-ferrite, after annealing at 1000 °C. The average grain sizes were found to be 13 and 19 nm for the as prepared samples synthesized at pH = 10.3 and pH = 10.9 respectively, which was increased with the increase in annealing temperature. Spontaneous magnetization values increased with the decrease in surface defects, whereas coercivity and remanence ratio showed peaks with increase in annealing temperature. The highest magnetic moments of 1.6μB and 2.1μB per molecule were observed at 60K for the tetragonal and cubic Cu-ferrite samples respectively. The highest anisotropy constant (K) of 4.98 × 103 and 16.0 × 103 J/m3 was observed at 60K for the sample prepared at pH = 10.3 and pH = 10.9 respectively. The nonsaturation parameter varies similarly with coercivity and anisotropy constant in these nanoparticle samples. The structural transformation, decrease in surface defects, and anisotropy variation with increasing annealing temperature and grain growth explains the observed magnetic properties. [Display omitted] •Cu-ferrite nanoparticle samples were synthesized by co-precipitation method at pH of 10.3 and 10.9 and were annealed.•Depending on pH of the solution different phases of Cu-ferrite were observed at higher annealing temperature of 1000 °C.•Formation of different phases influence the magnetic properties.•Nonsaturation of magnetic hysteresis loop decreases with the decrease in surface defects and anisotropy.•PH of the solution during synthesis and subsequent annealing tune the magnetic properties.