Tuning exchange bias in silica-coated Co-CoO core-shell nanostructure

Interface of core-shell Co-CoO nanostructure exhibits exchange bias (EB) phenomenon which arises due to the competition between ferromagnetic (FM) and antiferromagnetic (AFM) order at the interface. Here, in this manuscript, we study core-shell Co-CoO nanostructure and report an approach for tuning the EB field ( \(H_E\) $H_E$ ) and coercivity ( \(H_C\) $H_C$ ) via controlling interparticle separation which leads to variable interactions. The core-shell Co-CoO structure has been prepared in a conventional sol-gel route. Further, a variable amorphous non-magnetic silica (SiO \(_2\) ${}_2$ ) shell is coated over the nanoparticles via typical chemical synthesis to control the interparticle interaction. Analysis of powder X-ray diffraction (PXRD) data and transmission electron microscope (TEM) images confirms creation of SiO \(_2\) ${}_2$ -coated Co-CoO with average particle size \(\approx \) $\approx$ 18 nm. Studies on isothermal remanence magnetization (IRM) and dc demagnetization (DCD) indicate that the dipolar interaction among the nanoparticles varies inversely with interparticle separation. With increase in SiO \(_2\) ${}_2$ coating thickness, i.e., decrease in interparticle interactions, \(H_E\) $H_E$ and \(H_C\) $H_C$ decrease monotonically. These results open up the possibility of tuning EB by controlling interparticle interactions.