Magnetic properties of ordered array of nanobumps of [Co/Ni]4, 10, 20 multilayers

Abstract

Recently, bit patterned media (BPM) have been projected as one of the promising media for high density magnetic storage devices. In this work, we have studied the magnetic properties of Co/Ni multilayers-based BPM. Thin films of [Co(0.3 nm)/Ni(0.6 nm)]4, 10, 20 multilayers (MLs) were deposited on the barrier layer of an ordered array of nano-bump of anodic alumina (AAO) template using dc magnetron sputtering. From the measurement of room temperature magnetization hysteresis (M − H) curves, it is observed that [Co(0.3nm/Ni(0.6 nm)] nano bumps with N = 4 and 10 bi-layers exhibit magnetic isotropy behavior but, nanobumps with N = 20 bi-layers is found to display perpendicular magnetic anisotropy with an anisotropy constant (Ku) of 1.90 × 105 erg/cm3. The value of coercivity (HC) and squareness increases up to N = 10 bi-layers and then it further decreases for N = 20 bi-layer. The value of HC is found to be in the range of 100–200 Oe. The post-annealing of the nano-bumps enhances the coercivity but it destroys the perpendicular magnetic anisotropy. The obtained magnetic properties parameters on nano-bumps are compared with the properties of the same multilayers deposited on a flat Si substrate. It is observed that the values of HC for Co/Ni nanobumps was found to be higher in comparison to the films deposited on flat Si substrates, but squareness (MR/MS) and Ku were found to be lower.