SUPERPARAMAGNETIC RELAXATION OF FE DEPOSITED ON MGO(001)

Superparamagnetic behavior is investigated for Fe grown at 700 K onto MgO(001) to a thickness equivalent to that of a ten monolayer film. Tw o such Fe deposits separated by a 200-Angstrom deposit of MgO exhibit a ferromagnetic response with no hysteresis at either 300 or 150 K, bu t with identical reduced magnetization curves M(H/T) which confirms th e existence of superparamagnetism. M(H) data at 300 K were fitted to a Langevin function to yield an average particle size of 100 Angstrom d iameter. M(T) for held-cooled and zero-field-cooled samples shows beha vior characteristic of superparamagnetic particles with a distribution in particle size. Time-dependent remanent magnetization data measured over a 20 h period at various temperatures show nonexponential decay attributed to the distribution in particle size and interactions among the particles.