Exchange bias effects in Co3C/CoFe2O4 FM/FiM nanocomposites

Abstract

The exchange bias effects in hard/soft magnetic nanocomposites are of significant interest for spintronic and high-density data storage applications. However, to get stable exchange bias through interfacial coupling remains main challenge. Here, Co3C/CoFe2O4 FM/FiM nanocomposite is successfully synthesized via the polyol reduction method to investigate the role of interfacial exchange interactions between ferromagnetic Co3C and ferrimagnetic CoFe2O4 phases. The structural characterization confirmed the coexistence of both phases with nanoscale crystallinity, while magnetic measurements revealed strong temperature-dependent hysteresis behavior. A large coercivity of ∼7899 Oe at 50 K and ∼655 Oe at 300 K was observed, along with a clear exchange bias field of 6–169 Oe at 300–50 K, showing enhanced interfacial spin coupling. The zero-field-cooled and field-cooled magnetization curves showed a blocking temperature above 400 K, indicating strong magnetocrystalline anisotropy and significant interfacial exchange coupling in the nanocomposite. The observed exchange bias is attributed to exchange coupling between the hard CoFe2O4 phase and the ferromagnetic Co3C phase at their interfaces. The maximum energy density (BH)max of the nanocomposite ranges from 3 to 97 MGOe, and the magnetic anisotropy constant ranges from 0.1005 to 1.3879 × 105 Jm−3 at 300–50 K. This work is considered a first study of exchange coupling between a ferromagnetic metal carbide (Co3C) and a ferrimagnetic oxide (CoFe2O4), establishing how carbon at the magnetic interface modifies exchange anisotropy and reversal mechanisms in a rare-earth-free hard/hard bi-magnetic system. These findings open a route for a novel composite and its potential for spintronics and rare-earth-free magnets.