Dynamic spin freezing and magnetic memory effect in ensembles of interacting anisotropic magnetic nanoparticles
Korobi Konwar, S. D. Kaushik, Debasis Sen, Pritam Deb
Abstract
We explore the dependence of the magnetic memory effect on demagnetizing interactions by considering two differently organized ensembles of anisotropic ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$ nanoparticles: a compact ensemble (CE) and a hollow core ensemble (HCE). The dynamic magnetic behavior is extensively investigated by performing ac susceptibility, magnetic memory measurements, and dc magnetic aging protocols. The frequency dependence of the freezing temperature is analyzed with the help of two dynamic scaling models: the Vogel-Fulcher (VF) model and the power-law model. Both the systems exhibit a cluster spin-glass phase, as realized from the Mydosh parameter, VF temperature, relaxation time for single spin flip, and critical exponent. The progressive spin freezing is ensured by multiple intermediate metastable states and significant memory effects in both the systems. The presence of hollow core geometry with highly interacting surface nanoparticles and partially aligned magnetic easy axes leads to a complex anisotropic energy landscape in HCE. As a consequence, prominent magnetic memory effect is observed in HCE along with higher activation energy, reduced blocking temperature, and enhanced coercivity compared to CE.