Exchange-Biased Fe/FeF₂ Nanocomposites: Unveiling the Structural Insights into Spin-Dependent Tunnel Transport

Spin-dependent charge tunneling transport of magnetic nanocomposites under alternating current or direct current has revolutionized the understanding of the quantum-mechanical phenomenon in complex granular solids. The tunnel magnetodielectric (TMD) and tunnel magnetoresistance (TMR) effects are two critical functionalities in this context, where dielectric permittivity and electrical resistance, respectively, change in response to an applied magnetic field due to charge tunneling. However, the structural correlation between TMD and TMR, as well as the mechanisms, remains poorly understood, largely due to the challenges in directly characterizing nanoscale intergranular interactions. In this work, we fabricated a granular nanocomposite consisting of Fe nanogranules dispersed within an antiferromagnetic FeF₂ matrix. The exchange bias interaction between Fe and FeF₂ revealed a magnetic transition from superparamagnetic to antiferromagnetic and ferromagnetic behavior at low temperature. This study provides new insights into the interplay between spin-dependent tunneling and granular interactions, facilitated by the antiferromagnetic nature of the matrix─an interaction that is not achievable with conventional composites that use nonmagnetic matrices.