Superparamagnetic spin dynamics studied using selective excitation double Mossbauer spectroscopy

A detailed study of spin dynamics in a 6 nm Fe3O4 ferrofluid using a substa ntially improved selective excitation double Mossbauer (SEDM) experimental technique has led to the unambiguous separation of static disorder, collect ive excitations, and moment reversals. Superparamagnetic spin flips have be en observed through the appearance of an additional line in the SEDM spectr um, defining the energy transitions during relaxation, with frequencies of 2.5 +/- 0.3 MHz at 70 K to 9.7 +/- 1.0 MHz at 110 K. SEDM offers a precise window into the dynamics and blocking behavior of fine particle systems.