Direct observation of momentum-dependent exchange interaction in a heisenberg ferromagnet.
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.
Miyazaki
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H
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan. hmiyazak@ims.ac.jp
Ito
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T
Im
H J
HJ
Yagi
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Kato
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Soda
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Kimura
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