The relationship between high speed switching characteristics and the fluctuation field

Current thin film high performance media have very high viscosity and consequently a significant dependence of the remanent coercivity HCR on the measurement time. The fluctuation field Hf is a parameter commonly used to describe thermal effects and is defined in terms of the magnetic viscosity and the irreversible susceptibility χIRR. Previous work has shown that the viscosity is independent of time down to 10−8 s. Here we examine the time dependence of χIRR on a variety of particulate and high density thin film media at both long times (5–1000 s) and very short times (1–20 ns). It was found that χIRR was independent of time down to ∼10 ns. However, below 10 ns, χIRR decreased rapidly, signaling the probable onset of gyromagnetically controlled switching.