Influence of Tm and Tb co-substitution on structural and magnetic features of CoFe2O4 nanospinel ferrites

Tm-Tb co-substituted CoFe 2O4 nanospinel ferrites (CoTm xTbxFe2−2xO4, CoTmTb (x = 0.00– 0.03) NSFs)) were prepared via a sonochemical chemical route. The microstructures and morphologies of the NSFs were investigated via XRD, SAED and TEM/SEM, along with EDX techniques. The XRD analysis confirmed the cubic structure all the products along with the absence of any impurities. All the crystallite sizes were observed to be within the range of 9–11 nm. Electron microscopy techniques (SEM, TEM and HR-TEM) proved a cubic morphology in each case and their chemical compositions were confirmed by EDX. The magnetic properties of the synthesized NSFs were investigated via VSM through analysis of the magnetization versus applied magnetic field data. The M–H studies were made at 10 and 300 K. All the NSFs displayed soft ferrimagnetic behavior. It was observed that Tb3+ and Tm3+ ions substitutions provoke substantial variations in the magnetic behavior of the host CoFe 2O4 system. Upon doping the CoFe 2O4 system with the Tb3+ and Tm3+ ions, the magnetic features, Ms (saturation) and Mr (remanent) as well as the Hc (coercive field), increased for x=0.010 and then started to decrease gradually with a further increase in the dopant contents (Tb3+ and Tm3+ ions). The exchange interactions between the cations distributed over the A and B sites is one of the main reasons for the observed evolution in the magnetization magnitudes with the composition. Other factors, like strain, surface spins disorder, crystallite size, size of magnetic domains and Bohr magneton number, were also reported in order to explain the variations in diverse magnetic parameters.