Exhibition of magnetic memory effects and exchange bias in nanocrystalline CoSb2O4

Abstract

This article discusses the origin and exhibition of the exchange bias (EB) phenomenon and magnetic memory effect in a variety of time (t) and temperature (T) dependent protocols in nanocrystalline CoSb₂O₄ (CSO). The traditional hydrothermal technique was followed in the preparation of cuboid shaped nanoparticles. The as-synthesized sample was characterized well via powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM) studies revealing crystallite and particle sizes of ∼51 and ∼96 nm, respectively. Thermal variation of magnetization [M(T)] suggests creation of a canted antiferromagnetic (AFM) ground state with multiple magnetic transitions around 79, 50 and 11 K. Sizable orbital moment contribution has been validated from the mismatch between the experimental value and the theoretical estimation of the Curie–Weiss moment. Cooling field induced metastability below the first order magnetic transition and the explicit signature of the magneto-caloric-effect in terms of the change in entropy are two noteworthy features in this system. Below the ordering temperature, a substantial amount of EB (with EB field (H_E) = 800 Oe at 3 K with a 40 kOe cooling field) has been demonstrated through the shift in the magnetic hysteresis (M−H) loop when cooled in an external magnetic field. Exchange interaction originates due to the cumulative effect of disorder and competing interactions because of the coexistence of more than one type of spin order. Creation of a super-spin-glass (SSG) like state due to the finite size effect and a strong dipolar interaction in the nanoparticle assembly manifest the memory effect in M(T) in field-cooled (FC) and zero-field-cooled (ZFC) protocols along with isothermal remanent magnetization (IRM) mechanisms.