Evolution of frozen magnetic state in co-precipitated Zn delta Co1-delta Fe2O4 (0 <= delta <= 1) ferrite nanopowders

The evolution of frozen magnetic state of Zn delta Co1 - delta Fe2O4 (0 <= delta <= 1) ferrite nanoparticles was studied by applying vibrating sample magnetometer measurements in temperature range 5-350 K and magnetic fields up to 7 T. It was shown that gradual conversion from the inverse spinel (delta = 0) to the normal one (delta = 1.0) is correlated with a drop of freezing temperature T-f (corresponding to blocking of mean magnetic moment of the system) from 238 K (delta = 0) to 9 K (delta = 1.0) and with a decrease of magnetic anisotropy constant K-1 from about 8 . 10(5) J/m(3) to about 3 . 10(5) J/m(3). The percolation threshold predicted for bulk ferrites at 1 - delta approximate to 0.33 was observed as a significant weakness of ferrimagnetic coupling. In this case magnetization curves, determined according to the zero field cooling protocol, reveal two distinct maxima indicating that the system splits into two assemblies with specific ions distribution between A and B sites. (C) 2018 Elsevier B.V. All rights reserved.