Coercivity of disordered nanostructures

Zero- and finite-temperature coercivity mechanisms in disordered nanostructures are investigated by model calculations. Three different aspects are considered. First, it is shown that strongly reduced exchange in grain-boundary regions changes the power-law scaling exponent for the coercivity of random-anisotropy magnets. Second, it is analyzed how random interatomic exchange affects the thermal blocking and therefore the coercivity of spin glasses. Third, a master-equation approach is used to quantitatively elucidate the relation between the magnetic-viscosity regime and the sweep-rate dependence of the coercivity. A common feature of the considered mechanisms is that interatomic exchange creates nanoscale cooperative units which realize the coercivity in real space.