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/in 2 . By electroplating into Al 2 O 3 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 H s for these particles. At zero degrees, H s lies above the curling curve for R/R 0 > 4, and falls below the curling curve for R/R 0 <2, where R 0 is the exchange length ( R 0 = 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/R 0 ∼3.