SWITCHING IN SINGLE-DOMAIN NANOSTRUCTURES AT FINITE TEMPERATURES

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.