Ferromagnetic nanocrystalline Gd-doped ZnO powder synthesized by coprecipitation

A mixture of bi(acetylacetonato) zinc(II)hydrate and tri(dimethylglyoximato)gadolinium(III) complexes was used to synthesize Gd-doped ZnO powder. The synthesis was a result of the complexes’ thermal codecomposition. Magnetic characterizations have shown that the sample with the atomic ratio 3.5% Gd exhibited a clear ferromagnetic behavior at room temperature (RT) and demonstrated the highest saturation magnetization at 0.05 emu/g. When all the Gd ions were considered to be ferromagnetically coupled (successful doping) the analysis of moments per Gd atom resulted in a very low value (≈0.01 μB). However, when the uncorrelated spins that are responsible for the paramagnetic component were taken into account, the analysis of moment per Gd atom gave a high value (≈9 μB). These results led us to believe that successful but not complete doping may be responsible for the observed RT magnetization in these Gd doped ZnO systems. Further analysis for the irreversible component of the sample with 3.5% Gd has shown that the activated moment, upon reversal, is large (μact=1.78×106 μB). This result hints at the existence of largely correlated regions of spins. Moreover, the obtained distribution of activation energies demonstrates that the reversal mechanism cannot be due to independent regions of correlated spins. This result explains the low values of the remanence ratio and coercivity that are usually observed in such systems.