Fabrication and size dependent magnetic studies of NixMn1-xFe2O4 (x=0.2) cubic nanoplates

Nickel substituted manganese ferrite [NixMn1-xFe2O4 (x = 0.2)] nanoplates with cubic shape and controlled sizes were fabricated by chemical coprecipitation technique. Structural analyses confirmed the formation of single phase crystalline nanoplates in the size range 8-24 nm. Magnetic studies showed that coercivity as a function of plate length goes through a maximum, peaking at 162 Oe and then decreases for larger nanoplates, indicating that the single domain limit for NixMn1-xFe2O4 (x = 0.2) is similar to 21 nm. While negligible coercivity at below 10 nm confirms the superparamagnetic limit in the range 8-10 nm for these nanoplates. Saturation magnetization of the samples was found to increase linearly with plate length in the single domain regime, however this increase was observed slower for the larger nanoplates. Typical blocking effects were studied in the temperature range 20-300 K and it was found the superparamagnetic blocking temperature increases monotonically with increasing size of the nanoplates. The results are discussed in terms of the enhanced surface roles and variation of surface and effective anisotropies with size of the nanoplates that strongly influence their magnetic properties within the domain of Stoner Wohlfarth model for ferromagnetic systems. (C) 2016 Elsevier B.V. All rights reserved.