Time decay of remanent magnetization, remanent coercivity, and readback signal of ultra-thin longitudinal CoCr12Ta2 /Cr thin film media

The time decay of remanent magnetization, remanent coercivity, and readback signal of ultra-thin longitudinal CoCr₁₂Ta₂ /Cr thin film media have been studied experimentally with a VSM and a recording spin-stand tester using a MR read head. The time decay rate of the remanent magnetization or magnetic viscosity S increases significantly with decreasing magnetic layer thickness, especially for a M_rt of less than 0.5 memu/cm² and it is found to be strongly related to the strength of the magnetic interactions between grains. For such thin media (CoCrTa=6 nm) with a M_rt=0.36 memu/cm², the readback signal amplitude decreases at a high decay rate of about 5% per decade of time (sec) which is found to be essentially independent of the linear recording density from 2000 to 6000 fc/mm. To obtain CoCr₁₂Ta₂/Cr media with a time decay rate of less than 10% in 5 years, the value of the ratio of the anisotropy energy barrier to the thermal energy (Kv/kT) should be greater than 80 which corresponds to a CoCrTa thickness of greater than about 10 nm