![]() ![]() Co/CoO core-shell structure has been the model system for the EB effect, which was discovered in 1956 by Meiklejohn and Bean. This shift, measured by the exchange-bias field 'H EB ', appears after cooling the EB system in a magnetic field from temperatures above the NĂ©el temperature (T N) of the antiferromagnet. Exchange bias (EB) is a fundamental magnetic phenomenon that occurs when ferromagnetic (FM) and antiferromagnetic (AFM) heterogeneous structures interact, leading to shifts of the hysteresis loops along the field axis. These new findings provide a novel approach toward manipulating and fine-tuning the exchange bias effects in nanoscale systems for spintronics applications. ![]() Theoretical studies confirm that the emerging spin-glass state in the CoO shell has a significant impact on the exchange bias of the system. By improving the crystallinity of CoO shell by performing surface oxidation at an elevated temperature, the spin-glass ordering is suppressed by the antiferromagnetic ordering, resulting in a significantly lower exchange-bias field (2.2 kOe) and a prominent training effect due to the existence of multiple easy axes in the multi-crystalline CoO shell. At low temperatures, the developed spin-glass state with net magnetic moments in the CoO shell provides a unidirectional anisotropy in the Co core via exchange coupling, leading to a giant exchange bias field up to 3.6 kOe. In this report, the exchange-bias effect of Co/CoO core/shell nanoparticles with the amorphous CoO shell has been investigated. Finally, core/void/shell MNPs of 11.9 nm prior to the formation of the hollow MNPs showed a similar behavior, with non-negligible HEB, highlighting the importance of surface spins in EB generation. The existence of surface spins, present on the outer and inner surfaces, was demonstrated, and an intrinsic EB phenomenon (HEB = 444 Oe for hollow iron oxide-based MNPs of 13.1 nm) with significant magnetization (MS~50 emu/g) was obtained. Both HC and HEB present a maximum threshold above which their values begin to decrease with HFC, showing a new trend of HEB with HFC and allowing modulation on demand. The effect of external parameters on the coercivity (HC), remanence (MR), exchange bias field (HEB) and frozen spins, such as cooling field (HFC) and temperature, was investigated. The two mechanisms involved in EB generation were investigated: the frozen spins present in the nanograins that form the nanoparticles and the surface spins. In this work, we present the synthesis and study of the EB properties of iron-oxide-based hollow MNPs and their precursors Fe/iron oxide MNPs with core/void/shell structure. Exchange bias (EB) properties have become especially important in hollow magnetic nanoparticles (MNPs) due to the versatility and reduced size of these materials. ![]()
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