Hard Magnetic Properties of Nanocrystalline Cobalt-Phosphorus (Co_100-XP_X) Electrodeposits

Abstract

Nanocrystalline cobalt-phosphorus (Co100-xPx) thin films were electrodeposited and their extrinsic magnetic properties were systematically studied by controlling various synthesis parameters. The crystalline thin films exhibited the perpendicular anisotropy which had the behavior of stripe domains. The incorporation of phosphorus (P) atoms into cobalt (Co) lattice structure resulted in the transition from single to pseudo-domain particles. As P content augmented in the crystalline deposits, P precipitation at the grain boundary served as pinning sites, resulting in higher coercivity. Further increase in P content reduced the crystallinity of the deposits and thereby lowered perpendicular anisotropy and coercivity. Promotion of P content was observed at higher NaH2PO2 concentration, lower pH, and smaller film thickness. Temperature was also adjusted to tune P content by controlling the fraction of free Co2+ ions and complexes Co(NH3)x 2+ in solution.