title: Direct observation of momentum-dependent exchange interaction in a heisenberg ferromagnet.
abstract: We measured the temperature-dependent three-dimensional angle-resolved photoemission spectra of EuO (100) thin film, a typical Heisenberg ferromagnetic semiconductor, to investigate the essential origin of the ferromagnetic transition. We observed sizable energy dispersion and large binding-energy shift of the Eu 4f state below the Curie temperature only near the Gamma and X points, despite the expected Heisenberg-type local magnetism. The band dispersion and temperature dependence of the Eu 4f state indicates that the indirect exchange and superexchange interactions have strong momentum dependence. The observed temperature-dependent energy shift of the 4f state is the essential origin of the magnetism of EuO.
authors: UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan. hmiyazak@ims.ac.jp
authors: H
authors: H
authors: Miyazaki
authors: T
authors: T
authors: Ito
authors: H J
authors: HJ
authors: Im
authors: S
authors: S
authors: Yagi
authors: M
authors: M
authors: Kato
authors: K
authors: K
authors: Soda
authors: S
authors: S
authors: Kimura