Switching field studies of individual single domain Ni columns

Abstract

Quantitative measurements of the switching field properties of individual single-domain particles are both scientifically and technologically important. Such data are relevant for the engineering of a patterned magnetic storage medium where a single bit of information corresponds to individual single-domain particles with sizes consistent with storage densities >50 Gbit/in2. By electroplating into Al2O3 and track-etched polycarbonate filters, we have prepared particles over a large range of radii from R=20–500 nm, and have characterized them by transmission electron microscopy. Using a magnetic force microscope with an in situ electromagnet, we have quantified the extent to which the particles can be considered “single-domain.” We have also measured the angular dependence of the switching field Hs for these particles. At zero degrees, Hs lies above the curling curve for R/R0>4, and falls below the curling curve for R/R0<2, where R0 is the exchange length (R0=20.6 nm for Ni). At intermediate radii, the angular dependence data are close to the curling curve with a crossover of the data and the curling solution at R/R0∼3.