Magnetism of nanometer-scale iron particles arrays (invited)

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Abstract
The magnetization behavior in arrays of small ferromagnetic iron particles is investigated. Arrays were fabricated by a combination of chemical vapor deposition and scanning tunneling microscopy. This method allows a variety of particle arrays to be grown differing in particle height, diameter, or arrangement. Moreover, the arrays can be grown directly onto different materials such as Au or permalloy. Magnetic measurements were conducted by Hall magnetometery up to 100 K and compared to switching field measurements by means of magnetic force microscopy at room temperature. The magnetization reversal mechanisms were studied from magnetization curves measured for an arbitrary angle ϑ of the applied field with respect to the long axis of the particles. By analyzing the reversible rotation, the particles’ magnetic core diameter and the shape anisotropy could be determined. A phenomenological model based on thermally activated magnetization reversal was introduced and compared to experimental switching field dependences on temperature as well as on ϑ. Thermal effects may govern the magnetization reversal in particles of 10 nm diameter at all temperatures. For 14 nm particles and temperatures below 30 K, curling (for ϑ⩽30°) and homogeneous reversal modes appear to dominate.