title: Robust antiferromagnetic coupling in hard-soft bi-magnetic core/shell nanoparticles.
abstract: The growing miniaturization demand of magnetic devices is fuelling the recent interest in bi-magnetic nanoparticles as ultimate small components. One of the main goals has been to reproduce practical magnetic properties observed so far in layered systems. In this context, although useful effects such as exchange bias or spring magnets have been demonstrated in core/shell nanoparticles, other interesting key properties for devices remain elusive. Here we show a robust antiferromagnetic (AFM) coupling in core/shell nanoparticles which, in turn, leads to the foremost elucidation of positive exchange bias in bi-magnetic hard-soft systems and the remarkable regulation of the resonance field and amplitude. The AFM coupling in iron oxide-manganese oxide based, soft/hard and hard/soft, core/shell nanoparticles is demonstrated by magnetometry, ferromagnetic resonance and X-ray magnetic circular dichroism. Monte Carlo simulations prove the consistency of the AFM coupling. This unique coupling could give rise to more advanced applications of bi-magnetic core/shell nanoparticles.
authors.affiliation: 1] ICN2-Institut Catala de Nanociencia i Nanotecnologia, Campus UAB, E-08193 Bellaterra, Barcelona, Spain [2] Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Estrader
authors.affiliation: 1] ICN2-Institut Catala de Nanociencia i Nanotecnologia, Campus UAB, E-08193 Bellaterra, Barcelona, Spain [2] INSTM and Dipartimento di Chimica 'U. Schiff', Università degli Studi di Firenze, Via della Lastruccia 3, Sesto Fiorentino, I-50019 Firenze, Italy.
authors.forename: A
authors.initials: A
authors.lastname: López-Ortega
authors.affiliation: 1] LENS-MIND-IN2UB, Departament d'Electrònica, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona, Spain [2] TEM-MAT, SCT, Universitat de Barcelona, E-08028 Barcelona, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Estradé
authors.affiliation: 1] St Petersburg Nuclear Physics Institute, 188300 Gatchina, St Petersburg, Russia [2] Ioffe Physico-Technical Institute of the RAS, 194021 St Petersburg, Russia.
authors.forename: I V
authors.initials: IV
authors.lastname: Golosovsky
authors.affiliation: Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Salazar-Alvarez
authors.affiliation: IAMPPMN, Department of Materials Science, NCSR 'Demokritos', 153 41 Aghia Paraskevi, Attiki, Greece.
authors.forename: M
authors.initials: M
authors.lastname: Vasilakaki
authors.affiliation: IAMPPMN, Department of Materials Science, NCSR 'Demokritos', 153 41 Aghia Paraskevi, Attiki, Greece.
authors.forename: K N
authors.initials: KN
authors.lastname: Trohidou
authors.affiliation: 1] Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA [2] Departamento de Física Aplicada III & Instituto Pluridisciplinar, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Varela
authors.affiliation: Department of Physics, Miami University, Oxford, Ohio 45056, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Stanley
authors.affiliation: Department of Physics, Miami University, Oxford, Ohio 45056, USA.
authors.forename: M
authors.initials: M
authors.lastname: Sinko
authors.affiliation: Department of Physics, Miami University, Oxford, Ohio 45056, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Pechan
authors.affiliation: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Keavney
authors.affiliation: LENS-MIND-IN2UB, Departament d'Electrònica, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Peiró
authors.affiliation: Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Suriñach
authors.affiliation: Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain.
authors.forename: M D
authors.initials: MD
authors.lastname: Baró
authors.affiliation: 1] ICN2-Institut Catala de Nanociencia i Nanotecnologia, Campus UAB, E-08193 Bellaterra, Barcelona, Spain [2] Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain [3] Institució Catalana de Recerca i Estudis Avançats (ICREA), E-08010 Barcelona, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Nogués