Tuning the coercivity and exchange bias by controlling the interface coupling in bimagnetic core/shell nanoparticles

Abstract

In order to explore an alternative strategy to design exchange-biased magnetic nanostructures, bimagnetic core/shell nanoparticles have been fabricated by a thermal decomposition method and systematically studied as a function of the interface exchange coupling. The nanoparticles are constituted by a ∼3 nm antiferromagnetic (AFM) CoO core encapsulated in a ∼4 nm-thick CoZnFeO (x = 0-1) ferrimagnetic (FiM) shell. The system presents an enhancement of the coercivity (H) as compared to its FiM single-phase counterpart and exchange bias fields (H). While H decreases monotonically with the Zn concentration from ∼21.5 kOe for x = 0, to ∼7.1 kOe for x = 1, H exhibits a non-monotonous behavior being maximum, H ∼ 1.4 kOe, for intermediate concentrations. We found that the relationship between the AFM anisotropy energy and the exchange coupling energy can be tuned by replacing Co with Zn ions in the shell. As a consequence, the magnetization reversal mechanism of the system is changed from an AFM/FiM rigid-coupling regime to an exchange-biased regime, providing a new approach to tune the magnetic properties and to design novel hybrid nanostructures.

Exploring Exchange Bias Coupling in Fe3−δO4@CoO Core–Shell Nanoparticle 2D Assemblies

“…Moreover, this distance can be even larger if we consider the click assembly process which disfavors the formation of tightly packed assemblies. Furthermore, exchange bias is favored by low magnetic anisotropy energy of FiM cores and large interfacial coupling energy . Therefore, strong dipolar interactions would enhance the magnetic anisotropy of FiM cores and so, would compete exchange bias coupling.…”

Internal Structure and Magnetic Properties in Cobalt Ferrite Nanoparticles: Influence of the Synthesis Method

“…The successful employment of such NPs in technological applications depends on a careful control of the magnetic properties. It was shown, for example, that the magnetic moment and the effective anisotropy can be tuned precisely by controlling the size and shape of the nanocrystals or the magnetic coupling in multicomponent nanostructures . An important step in this direction has been achieved by the development of synthesis procedures that allow an accurate control of the size and morphology of the NPs, such as non‐aqueous thermal decomposition of organometallic compounds at high temperatures, that can overcome many limitations of traditional aqueous methods …”

Tunnel Magnetoresistance in Self-Assemblies of Exchange-Coupled Core/Shell Nanoparticles

“…[27] In this regard, an exciting possibility is the fabrication of devices based on self-assemblies of exchange coupled core/shell MNPs with tailored magnetic properties. [28] The coercive field in these systems can be finely modified through the interface magnetic coupling [29][30][31][32][33][34], the core size and shell thickness, [35][36][37] or the magnetic anisotropy of the components. [23,[38][39][40] Devices of this type should provide a way to manipulate at will the characteristic switching field of TMR by controlling the magnetic coupling across the core/shell interface.…”