title: Observation of two nondispersive magnetic excitations in NiO by resonant inelastic soft-X-Ray scattering.
abstract: We present high resolution (DeltaE=120 meV) resonant inelastic x-ray scattering data measured at the Ni L3 edge (2p_{3/2}-->3d) on the paradigmatic antiferromagnetic oxide NiO. Spectra reveal clear signatures of magnetic excitations at approximately 95 and approximately 190 meV whose energy seems independent from transferred momentum. These spectral features are well reproduced by a single Ni2+ ion model in an effective exchange field. Within this local model the two magnetic excitations are characterized by a variation of the atomic magnetic moment along the local ordering direction (DeltaS_{alpha}) of one and two units. The DeltaS_{alpha}=2 case has different nature from bimagnons observed in optical Raman spectra, for which DeltaS_{alpha}=0.
authors.affiliation: CNR-INFM Coherentia and Soft, Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, I-20133 Milano, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Ghiringhelli
authors.forename: A
authors.initials: A
authors.lastname: Piazzalunga
authors.forename: C
authors.initials: C
authors.lastname: Dallera
authors.forename: T
authors.initials: T
authors.lastname: Schmitt
authors.forename: V N
authors.initials: VN
authors.lastname: Strocov
authors.forename: J
authors.initials: J
authors.lastname: Schlappa
authors.forename: L
authors.initials: L
authors.lastname: Patthey
authors.forename: X
authors.initials: X
authors.lastname: Wang
authors.forename: H
authors.initials: H
authors.lastname: Berger
authors.forename: M
authors.initials: M
authors.lastname: Grioni