DYNAMICS OF AN INTERACTING PARTICLE SYSTEM - EVIDENCE OF CRITICAL SLOWING-DOWN

The dynamics of a magnetic particle system consisting of ultrafine Fe- C particles of monodisperse nature has been investigated in a large ti me window, 10(-9)-10(4) s, using Mossbauer spectroscopy, ac susceptibi lity, and zero field cooled magnetic relaxation measurements. By study ing two samples from the same dilution series, with concentrations of 5 and 6 x 10(-3) vol%, respectively, it has been found that dipole-dip ole interaction increases the characteristic relaxation time of the pa rticle system at all temperatures investigated. The results for the mo st concentrated particle assembly are indicative of collective magneti c dynamics and critical slowing down at a finite temperature, T-g appr oximate to 40 K. Close to and below the transition temperature, an agi ng phenomenon is observed, another manifestation of collective magneti c dynamics.