title: Tunability of exchange bias in Ni@NiO core-shell nanoparticles obtained by sequential layer deposition.
abstract: Films of magnetic Ni@NiO core-shell nanoparticles (NPs, core diameter d ≅ 12 nm, nominal shell thickness variable between 0 and 6.5 nm) obtained with sequential layer deposition were investigated, to gain insight into the relationships between shell thickness/morphology, core-shell interface, and magnetic properties. Different values of NiO shell thickness t(s) could be obtained while keeping the Ni core size fixed, at variance with conventional oxidation procedures where the oxide shell is grown at the expense of the core. Chemical composition, morphology of the as-produced samples and structural features of the Ni/NiO interface were investigated with x-ray photoelectron spectroscopy and microscopy (scanning electron microscopy, transmission electron microscopy) techniques, and related with results from magnetic measurements obtained with a superconducting quantum interference device. The effect of the shell thickness on the magnetic properties could be studied. The exchange bias (EB) field H(bias) is small and almost constant for ts up to 1.6 nm; then it rapidly grows, with no sign of saturation. This behavior is clearly related to the morphology of the top NiO layer, and is mostly due to the thickness dependence of the NiO anisotropy constant. The ability to tune the EB effect by varying the thickness of the last NiO layer represents a step towards the rational design and synthesis of core-shell NPs with desired magnetic properties.
authors.affiliation: CNR-NANO, via G. Campi 213/a, 41125 Modena, Italy. Dipartimento FIM, Università di Modena e Reggio Emilia, via G. Campi 213/a, 41125 Modena, Italy.
authors.forename: Maria Chiara
authors.initials: MC
authors.lastname: Spadaro
authors.forename: Sergio
authors.initials: S
authors.lastname: D'Addato
authors.forename: Paola
authors.initials: P
authors.lastname: Luches
authors.forename: Sergio
authors.initials: S
authors.lastname: Valeri
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Grillo
authors.forename: Enzo
authors.initials: E
authors.lastname: Rotunno
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Roldan
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Pennycook
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Ferretti
authors.forename: Elena
authors.initials: E
authors.lastname: Capetti
authors.forename: Alessandro
authors.initials: A
authors.lastname: Ponti