title: Length Scale of the Spin Seebeck Effect.
abstract: We investigate the origin of the spin Seebeck effect in yttrium iron garnet (YIG) samples for film thicknesses from 20 nm to 50  μm at room temperature and 50 K. Our results reveal a characteristic increase of the longitudinal spin Seebeck effect amplitude with the thickness of the insulating ferrimagnetic YIG, which levels off at a critical thickness that increases with decreasing temperature. The observed behavior cannot be explained as an interface effect or by variations of the material parameters. Comparison to numerical simulations of thermal magnonic spin currents yields qualitative agreement for the thickness dependence resulting from the finite magnon propagation length. This allows us to trace the origin of the observed signals to genuine bulk magnonic spin currents due to the spin Seebeck effect ruling out an interface origin and allowing us to gauge the reach of thermally excited magnons in this system for different temperatures. At low temperature, even quantitative agreement with the simulations is found.
authors.affiliation: Institute of Physics, Johannes Gutenberg-University Mainz, 55099 Mainz, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kehlberger
authors.affiliation: Department of Physics, University of Konstanz, D-78457 Konstanz, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Ritzmann
authors.affiliation: Department of Physics, University of Konstanz, D-78457 Konstanz, Germany.
authors.forename: Denise
authors.initials: D
authors.lastname: Hinzke
authors.affiliation: Institute of Physics, Johannes Gutenberg-University Mainz, 55099 Mainz, Germany.
authors.forename: Er-Jia
authors.initials: EJ
authors.lastname: Guo
authors.affiliation: Institute of Physics, Johannes Gutenberg-University Mainz, 55099 Mainz, Germany.
authors.forename: Joel
authors.initials: J
authors.lastname: Cramer
authors.affiliation: Institute of Physics, Johannes Gutenberg-University Mainz, 55099 Mainz, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Jakob
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Mehmet C
authors.initials: MC
authors.lastname: Onbasli
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Dong Hun
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Ross
authors.affiliation: Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.|Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, Kaiserslautern 67663, Germany.
authors.forename: Matthias B
authors.initials: MB
authors.lastname: Jungfleisch
authors.affiliation: Fachbereich Physik and Landesforschungszentrum OPTIMAS, Technische Universität Kaiserslautern, Kaiserslautern 67663, Germany.
authors.forename: Burkard
authors.initials: B
authors.lastname: Hillebrands
authors.affiliation: Department of Physics, University of Konstanz, D-78457 Konstanz, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Nowak
authors.affiliation: Institute of Physics, Johannes Gutenberg-University Mainz, 55099 Mainz, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Kläui