Formation of Pd Nanocluster Seeds by Electrochemical Process for Control of Magnetic Properties in Co/Pd Multilayered Film

Abstract

Pd cluster seeds for a double-layered perpendicular magnetic recording medium composed of a Co/Pd multilayered film and a CoZrNb soft magnetic underlayer (SUL) were fabricated with an electrochemical treatment. By immersing the SUL into an aqueous PdCl 2 solution, the substitution of Pd for Co at the surface of the SUL took place, which was caused by the difference in electrochemical redox potential between Pd and Co. Uniformly distributed Pd clusters with 8 nm in diameter were successfully formed with the treatment for the optimized duration. Use of the Pd clusters as the seeds for deposition of the Co/Pd multilayered film increased the perpendicular coercivity and reduced the size of magnetic cluster of the film. These results suggested that the Pd cluster seeds led to the formation of magnetically isolated Co/Pd multilayered grains, improving the magnetic properties of Co/Pd multilayered film.Index Terms-Co/Pd multilayered film, electrochemical treatment, island structure, Pd cluster seeds.

Microstructure of a Co/Pd multilayered perpendicular recording medium with Pd seeds prepared by electrochemical process

“…In the previous study, the Pd clusters formed by an electrochemical process were reported to show the similar texture to the sputter-deposited Pd (10 nm) seedlayer [6]. However, the crystalline orientations of Co/Pd multilayer deposited on them were quite different.…”

“…18 nm. From XPS and XRD analyses, the island-like structures were identified as the metal Pd with face-centered cubic (FCC) structure [6], which is hereafter called ''Pd cluster seeds''. Table 2 shows the values of perpendicular coercivity (H c ) and loop slope parameter, a; of media I and II.…”

“…In the previous study, we have attempted to deposit Pd metal seeds on a CoZrNb SUL surface by utilizing an electrochemical substitution which resulted from the difference in redox potential among Co, Zr, Nb and Pd [5]. By using this process, island-like Pd clusters with a diameter of less than 10 nm were densely formed only by immersing the SUL into PdCl 2 solution, and the Co/Pd multilayered film sputter-deposited on the SUL exhibited fine magnetic clusters [6]. In this study, the microstructure of media with the Pd metal clusters was investigated to clarify effects of the Pd metal clusters on the grain growth of Co/Pd multilayered film.…”

Magnetic Thin Films for Perpendicular Magnetic Recording Systems

“…Since the electrochemical substitution reaction takes place only at the interface between the surface and the electrolyte solution, a deposited metal is expected to form a very thin film or island-like clusters rather than a thick continuous film, which could be applicable to the seed for the double-layered media. In this section, the Pd formation on a Co-based Co-Zr-Nb SUL as the seed for the sputter-deposited Co/Pd perpendicular magnetization film using the substitution reaction caused by the difference in redox potential between Pd and Co is mainly described [30,31].…”

“…18 nm. From X-ray photospectroscopy and diffractometry, the island-like structure was identified as the Pd metal with fcc structure [30], which is hereafter called "Pd cluster seeds".…”