title: Direct observation of magnetic metastability in individual iron nanoparticles.
abstract: X-ray photoemission electron microscopy combined with x-ray magnetic circular dichroism is used to study the magnetic properties of individual iron nanoparticles with sizes ranging from 20 down to 8 nm. While the magnetocrystalline anisotropy of bulk iron suggests superparamagnetic behavior in this size range, ferromagnetically blocked particles are also found at all sizes. Spontaneous transitions from the blocked state to the superparamagnetic state are observed in single particles and suggest that the enhanced magnetic energy barriers in the ferromagnetic particles are due to metastable, structurally excited states with unexpected life times.
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, Villigen PSI 5232, Switzerland.
authors.forename: Ana
authors.initials: A
authors.lastname: Balan
authors.affiliation: Condensed Matter Theory Group, NUM, Paul Scherrer Institut, Villigen PSI 5232, Switzerland.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Derlet
authors.affiliation: Departament de Física Fonamental and Institut de Nanociència i Nanotecnologia (IN2UB), Universitat de Barcelona, 08028 Barcelona, Spain.
authors.forename: Arantxa Fraile
authors.initials: AF
authors.lastname: Rodríguez
authors.affiliation: Institute of Surface Chemistry and Catalysis, University of Ulm, 89069 Ulm, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Bansmann
authors.affiliation: Department of Physics, University of Konstanz, 78457 Konstanz, Germany.
authors.forename: Rocio
authors.initials: R
authors.lastname: Yanes
authors.affiliation: Department of Physics, University of Konstanz, 78457 Konstanz, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Nowak
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, Villigen PSI 5232, Switzerland.
authors.forename: Armin
authors.initials: A
authors.lastname: Kleibert
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, Villigen PSI 5232, Switzerland.
authors.forename: Frithjof
authors.initials: F
authors.lastname: Nolting