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The fabrication and magnetic properties of arrays of short nanowires are reviewed. The arrays consist of electrodeposited ferromagnetic cylinders with aspect ratios of up to 3 and diameters of 57–180 nm. Their hysteresis loops are characterized and their remanent states are related to the predictions of a three-dimensional micromagnetic model, which shows a transition from a single-domain ‘flower’ state to a lower-remanence ‘vortex’ state with increasing diameter. The shapes of the array hysteresis loops are governed by interactions between the particles. The switching fields of small Ni cylinders can be described using a dynamic micromagnetic model.

Macroscopic and microscopic switching characteristics are obtained for 100 nm period arrays of Ni nanomagnets with a mean switching field (coercive field) of 710 Oe. Magnetic force microscopy in combination with micromagnetic theory shows that inhomogeneities in the particle shapes result in an intrinsic standard deviation in switching fields of 105 Oe, while the interactions between neighboring nanomagnets broaden the distribution to 276 Oe, equivalent to a squareness of 0.8 in the bulk hysteresis loop. The switching field distribution is consistent with curling as the switching mechanism.

The magnetic properties of a 100-nm-period large-area array of regular, 30-nm polycrystalline nickel particles have been studied. The particles are found to reverse incoherently, and their hysteresis behavior has been compared with a computational model over a range of temperatures. Excellent agreement with the model is obtained, indicating that switching of the particles is dominated by the reversal of approximately 10-nm-diameter volumes within each particle. These switching volumes are identified with the columnar grains in the polycrystalline nickel, showing that the microstructure determines the magnetic behavior of the particles. This explains the anisotropy distribution and the onset of superparamagnetism in the sample. Incoherent reversal occurs even though the particles are only 1.5 times the exchange length in nickel, a size at which nearly uniform rotation is expected to occur if the particles were homogeneous.

The magnetic behavior of two different 100 nm period arrays of Ni pillars has been characterized using vibrating sample magnetometry and magnetic force microscopy. The samples have similar aspect ratios of approximately two but different particle dimensions, leading to differences in the strength of magnetostatic interactions. The experimental results were compared with a simulation based on an Ising-like simple interaction model.

Arrays of cylindrical magnetic particles have been made using interference lithography combined with electrodeposition. The cylinders are made from Ni, Co, CoP, or CoNi, with diameters of 57--180 nm, aspect ratios of 0.4--3, and array periods of 100--200 nm. The remanent states of the cylinders correspond to single-domain ``flower'' states or to magnetization vortices depending on the particle size and aspect ratio. Experimental data are in good agreement with a magnetic-state map calculated using a three-dimensional micromagnetic model, which shows the remanent state as a function of particle size and aspect ratio. The interactions between the particles, and their switching-field distribution, have been quantified.