Ab initio micromagnetic calculations for particles (invited)

We present the results of first-principles calculations of the magnetic behavior of particles of varying shapes (sphere, prolate spheroid, and rectangular particles of various aspect ratios) and sizes ranging from ≊0.1 to 10 μm. We use a numerical implementation of micromagnetics in which the only input quantities, aside from the particle geometry, are the material parameters and the magnetic history. We have obtained quantitative agreement with theory for spherical particles and qualitative agreement with experiment in the case of rectangular objects, and we have observed a variety of interesting reversible and irreversible phenomena accompanying magnetic reversal in all objects. We describe key aspects of the numerical implementation and survey selected results.