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

LAVORATO, GABRIEL; LIMA, ENIO; TROIANI, HORACIO E; ZYSLER, ROBERTO; WINKLER, ELIN

Nanoscale

Royal Society of Chemistry

Año: 2017

2040-3364

In order to explore an alternative strategy to design exchange-biased magnetic nanostructures, bimagneticcore/shell nanoparticles have been fabricated by a thermal decomposition method and systematicallystudied 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 Co1−xZnxFe2O4 (x = 0?1) ferrimagnetic(FiM) shell. The system presents an enhancement of the coercivity (HC) as compared to its FiMsingle-phase counterpart and exchange bias fields (HEB). While HC decreases monotonically with the Znconcentration from ∼21.5 kOe for x = 0, to ∼7.1 kOe for x = 1, HEB exhibits a non-monotonous behaviorbeing maximum, HEB ∼ 1.4 kOe, for intermediate concentrations. We found that the relationship betweenthe AFM anisotropy energy and the exchange coupling energy can be tuned by replacing Co2+ with Zn2+ions in the shell. As a consequence, the magnetization reversal mechanism of the system is changed froman AFM/FiM rigid-coupling regime to an exchange-biased regime, providing a new approach to tune themagnetic properties and to design novel hybrid nanostructures.