title: Enhancement of ferromagnetism by oxygen isotope substitution in strontium ruthenate SrRuO3.
abstract: The oxygen isotope effect of the ferromagnetic transition in itinerant ferromagnet strontium ruthenate SrRuO3with a Curie temperature Tcof 160 K is studied. We observed for the first time a shift of ∆Tc~ 1 K by oxygen isotope substitution of16O →18O in SrRuO3by precise measurements of DC and AC magnetizations. The results surprisingly lead to the noteworthy inverse isotope effect with negative coefficient α = -∂ lnTc/∂ lnM. The Raman spectra indicate that the main vibration frequency of16O at 363 cm-1shifts to 341 cm-1following oxygen isotope substitution18O. This shift is remarkably consistent with the Debye frequency being proportional to ∝ 1√M where M is the mass of an oxygen atom. The positive isotope shift of ∆Tccan be understood by taking account of the electron-phonon interaction.
authors.affiliation: Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Kawanaka
authors.affiliation: Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Aiura
authors.affiliation: Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito 310-8512, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Hasebe
authors.affiliation: Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito 310-8512, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Yokoyama
authors.affiliation: Department of Physics, Kindai University, 3-4-1 Kowakae, Higashiosaka, Osaka 577-8502, Japan.
authors.forename: Takahiko
authors.initials: T
authors.lastname: Masui
authors.affiliation: Faculty of Science, Ibaraki University, 2-1-1 Bunkyo, Mito 310-8512, Japan.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Nishihara
authors.affiliation: Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yanagisawa