Abstract
The surface and interface effects of small antiferromagnetic nanostructures are important on the modulation of their magnetic properties. In this report, temperature and particle size dependent magnetic exchange bias effect was investigated in BiFeO3 (BFO) nanoparticles that possess natural core-shell structure. Nonmonotonic variation of exchange bias field, interesting surface spin-glass state and improved exchange bias training effect are only obtained in 18 nm BFO particles. Based on comparative experiments on particles with different sizes, we found that the surface spins and the interaction among them show great effect on the interfacial exchange coupling of the core-shell structure, and thus are responsible for the peculiar exchange bias behavior in small BFO nanoparticles. Our work provides the effect of surface spin state on the magnetic characteristics of nanomaterials and will favor their applications on spintronic devices.
Highlights
BiFeO3 (BFO) has received considerable attention as one of the most important single-phase multiferroics because of its high ferroelectric Curie temperature (Tc) of about 1103 K and antiferromagnetic Néel temperature (TN) of about 643 K1–6
The magnetic hysteresis loops exhibit a small shift along the magnetic field axes, implying the presence of an exchange bias effect in 18 nm BFO particles even in zero-field cooling (ZFC) condition
We have investigated the temperature and size dependent exchange bias behavior of BFO nanoparticles with natural core-shell structure
Summary
BiFeO3 (BFO) has received considerable attention as one of the most important single-phase multiferroics because of its high ferroelectric Curie temperature (Tc) of about 1103 K and antiferromagnetic Néel temperature (TN) of about 643 K1–6. Exchange bias effect was observed in BFO and its doped particles, and the results obtained by different research groups reveal that both the magnitude of the exchange bias field (HE) and its temperature-dependent behavior show obvious sample dependence[12,19,20,21,22]. Temperature-dependent nonmontonic variation of HE along with improved training effect is observed only in 18 nm BFO particles. Such interesting behavior is considered to be closely to its enhanced surface anisotropy and the presence of surface spin-glass state
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