Compositional control of the effective magnetic anisotropy in Mn and Co substituted spinel nanoparticles.

It has been shown through density functional theory (DFT) calculations that the magnetocrystalline anisotropy (MAE) for iron-based spinel nanoparticles can be altered through the addition of varying amounts of transition metals into their spinel structures. In this work, seven monodisperse spherical nanoparticle series were synthesized with varying amounts of Fe, Mn, and Co to target specific effective anisotropy (Keff) values that were calculated using DFT, giving the formula: Fe3-x-yMnxCoyO4. The Keff values determined from DC magnetometry ranged from 46-128 kJ m-3, increasing upon the addition of Mn, and increasing upon the addition of Co, verifying the trend that the DFT simulations predicted. The Keff value determined from DC magnetometry was lower than that predicted by DFT for the spinel nanoparticles with high cobalt substitution, and comparable for the other samples. From the AC susceptibility data, the trend in the anisotropy strength amongst the series of seven particles matched that extracted from the DC magnetometry data. Through these findings, it is shown that Keff is tunable by altering cationic ratios in spinel nanoparticles.