Exchange bias effect in ball milled Co–Cr 2O 3 FM–AFM nanocomposites

Abstract

Exchange coupled nanocomposite powders (Co) x (Cr 2O 3) 1− x consisting of mixture of ferromagnetic (FM) Co and antiferromagnetic (AFM) Cr 2O 3 have been prepared by mechanical ball milling. Upon field cooling, going through the Neel temperature, T N ∼ 307 K, of Cr 2O 3, a hysteresis loop shift, coercivity, and remanence enhancement were observed; effects indicative of the presence of exchange bias field ( H E) between the FM–AFM phases of the composite. The temperature dependent exchange bias field measurement shows that the exchange bias field reduces to zero at temperature T < ∼200 K < T N (307 K) of Cr 2O 3. However, since FM nanoparticles remain magnetic above T N (Cr 2O 3), the coercivity remains finite up to the room temperature. The role of interparticle interaction over surface spin disorder effects is also assessed by varying the FM/AFM ratio. The surface-spin disorders and dipolar interaction influence the magnetic properties of the composite at low and high FM content of the composite, respectively. The present study has potential implication of improving magnetic properties of hard-magnetic materials upon milling with antiferromagnetic materials.