Novel soft-magnetic underlayer of a bit-patterned media using CoFe-based amorphous alloy thin film

With the aim of applying to a soft-magnetic underlayer of the new type of bit-patterned media using nano-patterned glassy alloy thin film, (CoFe)–B–Si–Nb alloy thin films were deposited on a Si substrate by a DC magnetron sputtering method. The deposited thin films with the compositions of Co77Fe5B15Si2Nb1 and Co75Fe5B14Si5Nb1 were confirmed as a fully amorphous structure. The obtained Co77Fe5B15Si2Nb1 amorphous alloy thin film containing lower metalloid content exhibits extremely smooth surface and good soft-magnetic properties such as high saturation flux density of 1.2 T, in-plane low coercivity of 36 A/m, nearly zero-magnetostriction of 4 × 10−7 and high real part of permeability of 870 at 291 MHz, suggesting that the film is appropriate for the soft-magnetic underlayer. Moreover, a prototype bit-patterned media was prepared by utilizing the obtained thin film as a soft-magnetic underlayer. As a result of static tester measurements with a commercial perpendicular magnetic head, accurate information reading and writing on the prototype bit-patterned media were confirmed. It is therefore said that the Co77Fe5B15Si2Nb1 amorphous alloy thin film is a candidate material for the soft-magnetic underlayer of the new type of bit-patterned media.