title: The dipole moment of the spin density as a local indicator for phase transitions.
abstract: The intra-atomic magnetic dipole moment - frequently called ⟨Tz⟩ term - plays an important role in the determination of spin magnetic moments by x-ray absorption spectroscopy for systems with nonspherical spin density distributions. In this work, we present the dipole moment as a sensitive monitor to changes in the electronic structure in the vicinity of a phase transiton. In particular, we studied the dipole moment at the Fe(2+) and Fe(3+) sites of magnetite as an indicator for the Verwey transition by a combination of x-ray magnetic circular dichroism and density functional theory. Our experimental results prove that there exists a local change in the electronic structure at temperatures above the Verwey transition correlated to the known spin reorientation. Furthermore, it is shown that measurement of the dipole moment is a powerful tool to observe this transition in small magnetite nanoparticles for which it is usually screened by blocking effects in classical magnetometry.
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Straße 15, D-12489 Berlin, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Schmitz
authors.affiliation: 1] Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany [2].
authors.forename: C
authors.initials: C
authors.lastname: Schmitz-Antoniak
authors.affiliation: Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Warland
authors.affiliation: 1] Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany [2].
authors.forename: M
authors.initials: M
authors.lastname: Darbandi
authors.affiliation: Division of Materials Theory, Department of Physics and Astronomy, Uppsala University, Box-516, SE 75120 Uppsala, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Haldar
authors.affiliation: Division of Materials Theory, Department of Physics and Astronomy, Uppsala University, Box-516, SE 75120 Uppsala, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Bhandary
authors.affiliation: Division of Materials Theory, Department of Physics and Astronomy, Uppsala University, Box-516, SE 75120 Uppsala, Sweden.
authors.forename: O
authors.initials: O
authors.lastname: Eriksson
authors.affiliation: Division of Materials Theory, Department of Physics and Astronomy, Uppsala University, Box-516, SE 75120 Uppsala, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Sanyal
authors.affiliation: Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, Lotharstr. 1, D-47048 Duisburg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Wende