2020同步年報

Neutron Science 079 The same measurement results at 5 K and 200 K are plot- ted on a linear scale ( Fig. 2 ). The center signals at 0 meV overlap perfectly whereas the signal about 0.7 meV at 5 K disappears at 200 K. This observation confirmed a magnon peak and also showed a successful breaking of the concept of an inability to measure INS of films. Using the present identified magnon signal, they further obtained a dispersion curve, in Fig. 3 . Fitting the data points with the dispersion relation yielded J = 1.88 meV. This magnon band gap 0.32 meV is much smaller than Itoh’s 2 meV 2 and slightly smaller than 1 meV estimated from a FMR measurement calculated from the anisotropy energy estimated with bulk magnetization. In summary, Chou and his collaborators successfully demonstrated that measuring a low-energy excitation with inelastic neutron scattering on a single crystal film is pos- sible. Because of the strong strain effect at the STO/SRO interface, the crystal structure of SRO was tuned to a tetrag- onal structure with out-of-plane lattice parameter slightly larger than the in-plane lattice parameter, about 0.1%. This change suppresses the structural distortion and symmetry and produces a smaller magnon gap. (Reported by Chun- Ming Wu) This report features the work of Hsiung Chou and his collab- orators published in Physical Review B 101 , 054403 (2020). ANSTO SIKA − Cold Neutron Triple-axis Spectrometer • INS • Ferromagnetism, Magnon, Inelastic Neutron Scattering, Epitaxial Single-Crystal Thin Film References 1. G.-D. Dwivedi, C.-M. Wu, B.-Y. Chen, S. T. Lin, W.-Z. S. J. Qiu, G.-X. Sun, J.-W. Lynn, J.-W. Chiou, C.-H. Lee, W.-H. Li, S.-I. Yano, H. Chou, Physical Review B 101 , 054403 (2020). 2. S. Itoh, Y. Endoh, T. Yokoo, S. Ibuka, J.-G. Park, Y. Kaneko, K.-S. Takahashi, Y. Tokura, N. Nagaosa, Nat. commun 7 , 11788 (2016). Fig. 3 : (a) Relation between E and L (or Q). The magnon spectrum follows the dispersion relation (E ∝ Q 2 ). The data points presented as red circles are obtained from Ref. 2. The data points obtained from Chou’s measurements match well with Ref. 2 and are situated well within their FWHM. (b) Magnon dispersions for varied Coulomb U at temperature T = 0. Magnetic coupling J = 0.5 meV Å -3 , conduction-band electron density n e = 1 × 10 -4 Å -3 and Ru occupation c Ru = 10 -3 Å -3 . [Reproduced from Ref. 1]