Magnetic Properties of Electrodeposited Cobalt-Platinum (CoPt) and Cobalt-Platinum-Phosphide (CoPtP) Thin Films

CoPt and CoPtP thin films were synthesized using direct current (DC) aqueous electrodeposition from weak alkaline solutions. The basic plating solutions of binary CoPt thin films consisted of cobalt pyrophosphate [Co₂P₂O₇] and chloroplatinic acid [H₂PtCl₆]. Various amounts of sodium hypophosphite [NaH₂PO₂] was added to deposit ternary CoPtP thin films. The film composition was adjusted by varying the several electrodeposition parameters including electrolyte composition, solution pH, and current density and correlated to their microstructure and magnetic property (i.e. coercivity and squareness). For the binary CoPt thin films, the maximum coercivities [in-plane coercivity (H_c,//) = ∼1,600 Oe, and perpendicular coercivity (H_c,⊥) = ∼2,500 Oe] were obtained from electrolytes containing 0.01 M H₂PtCl₆ + 0.04 M Co₂P₂O₇ at current density (CD) of 7.5 mA cm^-2. In the case of ternary CoPtP electrodeposits, the maximum coercivities (H_c,// = ∼2,600 Oe, and H_c,⊥ = ∼3,800 Oe) were achieved from baths containing 0.015 M H₂PtCl₆, 0.07 M Co₂P₂O₇, 0.8 M NaH₂PO₂ at CD of 7.5 mA cm^{- 2} and solution pH 9. It was suggested that microstructure and magnetic properties are affected not only by the type of substrate but also by chemical compositions and electrodeposition conditions.