  Hall crosses were used to measure the magnetic properties of arrays of
ferromagnetic, nanometer-scale iron particles. The arrays typically consist of
several hundred particles of 9 -- 20 nm in diameter. It is shown that the
sensitivity of the measurements can be improved by matching the areas of the
Hall cross and the array grown onto it by at least an order of magnitude. We
predict that single particles of diameter as small as 10 nm can be measured if
grown onto a Hall cross of appropriate size.
