Preparation of nano-structured perpendicular magnetic recording media using porous alumina

点击翻译按钮获取中文摘要

Porous aluminum oxide layers or alumite layers were formed by anodic oxidizing high-purity aluminum sheets. The anodic oxidization in sulfuric acid solution resulted in the formation of micro pores 15 nm in diameter and 40 nm in center-to-center separation. First, we deposited cobalt-platinum alloy into the pores by pulse electroplating. The cobalt content increased with increasing pulse voltage. The squareness of perpendicular magnetization curve ranged from 0.6 to 0.7. We found that the squareness drastically increases to values exceeding 0.9 by applying platinum seed. The application of platinum seed also resulted in an increase in coercivity. The platinum seed was found to influence the crystallographic orientation of hcp cobalt-platinum alloy, enhancing the perpendicular anisotropy. Next, the effect of platinum seed on magnetic properties was compared with that of copper seed by depositing cobalt on them. The platinum seed enhanced the coercivity from 1.6 kOe without any seed to 2.5 kOe, while the copper seed increased it to 2.0 kOe. The squareness as high as 0.95 was attained using either of platinum or copper seed. The reason is not clear why the coercivity is more enhanced by the platinum seed than copper seed. Finally, we deposited iron-platinum alloy into the pores in order to investigate the feasibility of forming ordered equi-atomic iron-platinum alloy. The alloy composition deposited into the pores depended on bath composition and pulse voltage. Higher pulse voltages result in higher iron contents. The coercivity as well as squareness became higher with an increase in iron content. The films with nearly equi-atomic compositions were annealed in vacuum. Although the coercivity was enhanced by annealing, the formation of ordered iron-platinum alloy was not confirmed. More accurate analysis of alloy composition seems required to prepare alumite films containing equi-atomic iron-platinum alloy.