Exploring Exchange Bias Coupling in Fe_3−δO₄@CoO Core–Shell Nanoparticle 2D Assemblies

Abstract

Core-shell ferro(i)magnetic@antiferromagnetic (F(i)M@AFM) nanoparticles exhibiting exchange bias coupling are very promising to push back the superparamagnetic limits. However, their intrinsic magnetic properties can be strongly affected by interparticle interactions. This work reports on the collective properties of Fe 3-d O 4 @CoO core-shell nanoparticles as function of the structure of their assembly. The structure of nanoparticle assembly is controlled by a copper (I) catalyzed alkyne-azide cycloaddition (CuAAC) "click" reaction between complementary functional groups located at the surface of both substrates and nanoparticles. 2D arrays of nanoparticles with tunable sizes ranging from clusters of few nanoparticles to a dense and homogenous monolayer were prepared. The spatial arrangement of nanoparticles strongly influences the exchange bias coupling which is significantly enhanced for large 2D nanoparticle assemblies and, even more in 3D assemblies such as powder, which favour weak and random dipolar interactions.

Large structure-dependent room temperature exchange bias in self-assembled BiFeO3 nanoparticles

“…14). Therefore, contrary to the observations made by others 46,47 , the magnetic properties, in the present case, are primarily governed by surface spins and not by dipolar or exchange interactions among the particles.…”

“…The effective magnetic field produced by surface spin pinning is actually responsible for the variation in H E . When superstructure of nanoparticles are produced artificially, their magnetic properties are modified significantly (compared to isolated nanoparticles) due to exchange and dipolar interactions 46,47 between particles. But, in the present case, functionalization of particle surface as well as formation of different structures are effected together by the solvents.…”

A Detailed Investigation of the Onion Structure of Exchanged Coupled Magnetic Fe3−δO4@CoFe2O4@Fe3−δO4 Nanoparticles

“…As long as the size distribution of CS is rather narrow, it may results from inhomogeneous spatial distribution and weaker dipolar interactions which may be partially due to the oleic acid. 72 For CSS, the increase of magnetization at temperature higher than Tmax can be ascribed to super magnetic domains resulting from strong dipolar interactions between nanoparticles, e.g. superferromagnetism.…”

Structure, morphology and magnetic properties of flowerlike γ-Fe2O3@NiO core/shell nanocomposites synthesized from different precursor concentrations

“…The conventional exchange coupling between antiferromagnet (AFM) and ferromagnet (FM) or ferrimagnet (FiM) occurs at the F(i)M-AFM interface, where the hysteresis loop shifts (i.e., H E ) along the field axis after field cools down from above the Néel temperature (i.e., T N ) of AFM. For instance, the EB coupling exhibited by Fe 3-δ O 4 @CoO core/ shell nanocomposites is closely correlated to their assembly structure, accompanied by the strong influence of interparticle interaction on their intrinsic magnetic properties [11]. The study on 50 nm CoCr 2 O 4 particles with core/shell structure reveals that memory effect and EB effect are temperature-dependent [12].…”