We study the finite temperature magnetization reversal of single domai
n nanostructures (particles and wires) of different materials with Mon
te Carlo and analytic techniques. The temperature, angular, and shape
dependences of the switching field are calculated. For large structure
diameters, there are different reversal mechanisms at different orien
tations of the external field. For small structure diameters growth us
ually starts with the nucleation and a subsequent depinning of domain
walls at the end(s) of the structure. The nucleation energy of the dom
ain wall in a magnetic field approaches zero near the coherent rotatio
n limit at small aspect ratios and at fields less than the coherent ro
tation limit at large aspect ratios. As the domain wall energy approac
hes zero the domain wall width can remain finite. For small diameters
there is a significant temperature dependence in the coercive field. F
or structures whose easy crystalline anisotropy axis is not along the
major axis, a variety of switching scenario is observed. (C) 1995 Amer
ican Institute of Physics.