A paradigm of topological-microstructure-transition induced magnetic critical behaviors in percolative nanocomposites

Abstract

A study on the magnetic properties of the BaTiO3(BTO)-NiZnFeO4(NZFO) nanocomposite thin films is presented to reveal the effect of percolation and resultant topological-microstructure-transition on the magnetic properties of the nanocomposites, which exhibit a critical behavior at the percolation threshold fc. An in-depth analysis was conducted from the perspectives of chemistry and physics both experimentally and theoretically by considering the microstructure and magnetic parameters of the nanocomposites. The results show that the anomalous behavior of the coercivity is jointly controlled by the exchange interaction between the ferrite nanoparticles and the grain size associated with the topological microstructure and composition of the nanocomposites. When the NZFO content is below the percolation threshold, the coercivity is mainly controlled by grain size, and the permeability is controlled by the equivalent demagnetizing field. When the NZFO content is above the percolation threshold, the coercivity is jointly affected by exchange interaction and grain size, while the suppression of the permeability by the equivalent demagnetizing field is greatly reduced. The findings may help establish a new paradigm of topological-microstructure-transition induced magnetic critical behaviors of percolative functional composites, and more and more evidences suggest that such effect may widely exist in various percolative systems.