Nanostructured magnetic recording media by patterning and glancing angle deposition
In order to solve the trilemma problems that perpendicular magnetic recording is facing, advanced approaches such as heat assisted magnetic recording and bit patterned media are being intensively researched. In this work, high coercivity magnetic materials have been studied in the form of nanostructured Co/Pd and FeB/Pt multilayers. Arrays of uniformly spaced nanopillars over large areas were formed by utilizing block copolymer patterning. Uniform nanorods were formed by glancing angle deposition, a unique single-step approach to bit-patterned media. First, a detailed study on Co/Pd multilayered thin films was carried out to optimize the magnetic properties with respect to the thickness ratio, number of bilayers and seed layers. Then a statistical optimization of the patterning of Co/Pd multilayers by nanosphere lithography and block copolymer templating was carried out. The highest measured perpendicular anisotropy for Co/Pd films was 2.8 x 106 ergs/cm3. However, many of the M-H loops for Co/Pd were not saturated at the maximum field of 18 kOe, so the perpendicular anisotropy approaches 107 ergs/cm3. A unique single-step approach to nanostructuring these Co/Pd multilayers was developed: glancing angle deposition (GLAD), which produced Co/Pd nanorods with a coercivity as high as 2.9 kOe, a 123% increase over the flat multilayers. For deposition of FeBPt based granular media, two different techniques were used to sputter FeB/Pt multilayers. A finely alternated layered structure was proven to be more effective in forming L10 structured B-doped FePt. The FeBPt films thus formed were also patterned by block copolymer templating, and their magnetic properties were studied as a function of ion milling and annealing conditions. The highest coercivity achieved for patterned and annealed B-doped FePt films was 14 kOe.