title: Metamagnetic behavior and Kondo breakdown in heavy-fermion CeFePO.
abstract: We report that nonmagnetic heavy-fermion (HF) iron oxypnictide CeFePO with two-dimensional XY-type anisotropy shows a metamagnetic behavior at the metamagnetic field H(M)≃4  T perpendicular to the c axis and that a critical behavior is observed around H(M). Although the magnetic character is entirely different from that in other Ce-based HF metamagnets, H(M) in these metamagnets is linearly proportional to the inverse of the effective mass, or to the temperature where the susceptibility shows a peak. This finding suggests that H(M) is a magnetic field breaking the local Kondo singlet, and the critical behavior around H(M) is driven by the Kondo breakdown accompanied by the Fermi-surface instability.
authors.affiliation: Department of Physics, Graduate School of Science, Kyoto University, Kyoto, Japan. shunsaku@scphys.kyoto-u.ac.jp
authors.forename: S
authors.initials: S
authors.lastname: Kitagawa
authors.forename: H
authors.initials: H
authors.lastname: Ikeda
authors.forename: Y
authors.initials: Y
authors.lastname: Nakai
authors.forename: T
authors.initials: T
authors.lastname: Hattori
authors.forename: K
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authors.lastname: Ishida
authors.forename: Y
authors.initials: Y
authors.lastname: Kamihara
authors.forename: M
authors.initials: M
authors.lastname: Hirano
authors.forename: H
authors.initials: H
authors.lastname: Hosono