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 ) and coercivity ( 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 ) 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 -coated Co-CoO with average particle size ≈ 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 coating thickness, i.e., decrease in interparticle interactions, H_E and H_C decrease monotonically. These results open up the possibility of tuning EB by controlling interparticle interactions.