On the ferrite-controlled iron coupling for enhanced soft magnetic hybrid composites via first-order reversal curves

The substitution of conventional non-magnetic binder in soft magnetic iron composites by insulating spinel ferrite has been proven as a powerful avenue for enhancing the interparticle coupling while suppressing eddy currents. The inherent shortcomings of macroscopic characterization, hindering the phase-and magnetization process-resolved reconstruction, are overcome by generalized application of the first-order reversal curves analysis for the first time. The mechanism of involving ferrite coating as a true matrix, evolving from the beneficial coupling effect at low concentrations towards the reappearing demagnetizing interactions that trigger a partial decoupling at higher fractions, is evidenced in the computed diagrams encompassing the microscopic switching. This substantial improvement is related to a thin and uniform layer of submicron ferrite grains, occupying less than 5 vol% of bulk composite, which compensates the free magnetic poles at the surface of iron particles and restrains the action of local anisotropic demagnetizing field. A significant constriction of switching and interaction field distributions in ferrite-coated iron composites with respect to a ferrite-free system is modeled and the conditions for having amplified interphase coupling are defined. We further demonstrate that heterogeneous switching of core particles and their shell provides an efficient way of manipulating the domain walls activity with increasing prevalence of spin rotations with excessive content of ferrite.