Collective states of interacting ferromagnetic nanoparticles

TL;DR

This study investigates the collective magnetic behaviors of ferromagnetic nanoparticles embedded in an insulating matrix, revealing phase transitions from superspin glass to superferromagnetic states through experimental and simulation methods.

Contribution

It provides new insights into the phase diagram and criteria for identifying different collective magnetic states in nanoparticle systems.

Findings

Observation of superspin glass and superferromagnetic states with increasing particle density

Phase diagram resembling dilute disordered ferromagnet behavior

Criteria established for phase identification

Abstract

Discontinuous magnetic multilayers [CoFe/Al2O3] are studied by use of magnetometry, susceptometry and numeric simulations. Soft ferromagnetic Co80Fe20 nanoparticles are embedded in a diamagnetic insulating a-Al2O3 matrix and can be considered as homogeneously magnetized superspins exhibiting randomness of size (viz. moment), position and anisotropy. Lacking intra-particle core-surface ordering, generic freezing processes into collective states rather than individual particle blocking are encountered. With increasing particle density one observes first superspin glass and then superferromagnetic domain state behavior. The phase diagram resembles that of a dilute disordered ferromagnet. Criteria for the identification of the individual phases are given.