Perpendicular magnetization performance of hcp-cobalt nanocylinder array films electrodeposited from an aqueous solution containing cobalt (II)–citrate complexes

Abstract

According to the potential–pH diagram for the Co2+–citrate–H2O system, Co2+–citrate complexes are stable at a pH ranging from 3 to 9. Titration curves and ultraviolet–visible absorption spectra confirm that the pH buffer associated with the formation of Co2+–citrate complexes is active at a solution pH ranging from 3 to 9. In this study, hcp-Co nanocylinder arrays were synthesized by electrodeposition into nanochannels of anodized aluminum oxide templates using an aqueous solution containing citric acid. Due to the formation of Co2+–citrate complexes, the growth rate of the Co nanocylinders significantly decreases in solution containing citric acid compared with that containing boric acid. The axial direction of Co nanocylinder arrays, which were electrodeposited using an aqueous solution containing citric acid, is consistent with the c-axis of the hcp-Co crystal. The synergistic contribution of the magnetic shape and magnetocrystalline anisotropies improves the uniaxial magnetization performance of the Co nanocylinder arrays. When the c-axis orientation of the hcp-Co crystal is increased, the coercivity and squareness of Co nanocylinder arrays increase up to 2.13kOe and 0.84, respectively, at room temperature.