Abstract
The unexpected appearance of magnetic hysteresis and exchange bias effects in nominally antiferromagnetic NiO nanoparticles is usually explained in terms of a core/shell morphology, where a spin glass-like shell is exchange coupled to an antiferromagnetic core. However, recent studies have challenged the validity of this assumption for small enough NiO nanoparticles. In this work we present proof of the core/shell model for NiO nanoparticles with sizes below 10 nm by combining neutron powder diffraction and magnetic measurements. In addition, we have verified that the exchange bias effect persists even when the particle size is reduced down to 4 nm.
Highlights
In the recent years, magnetic nanoparticles (NPs) have attracted an intense research effort because they appear to play by a different set of rules compared to those governing bulk materials [1]
In this work we have performed a neutron powder diffraction and magnetometry joint investigation in order to check the correlation between the core/shell morphology and the occurrence of the exchange bias (EB) effect in NiO NPs with sizes below 10 nm
The fit of size histograms to lognormal distributions provides values for average NP diameter and standard deviation, D(σ), of 4(1) nm and 9(1) nm for samples NiO-4nm and NiO-9nm, respectively
Summary
Magnetic nanoparticles (NPs) have attracted an intense research effort because they appear to play by a different set of rules compared to those governing bulk materials [1]. One of the most remarkable consequences of this core/shell morphology is the occurrence of the exchange bias (EB) effect.
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