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The 250th SPring-8 Seminar

Subtitle/Subject Inelastic neutron scattering investigations of an anisotropic hybridization gap in the Kondo insulators: CeT2Al10 (T=Fe, Ru and Os)
Period from 14:00 to 15:00 Wed., Jul 13 , 2016
Venue Kamitsubo Hall
Host/Organizer JASRI
Format Lecture

Speaker : Dr Devashibhai Adroja

Language : English

Affiliation : ISIS Facility, Rutherford Appleton Laboratory

Title : Inelastic neutron scattering investigations of an anisotropic hybridization gap in the Kondo insulators: CeT2Al10 (T=Fe, Ru and Os)

The recent discovery of topological Kondo insulating behaviour in strongly correlated electron systems has generated considerable interest in Kondo insulators both experimentally and theoretically. The Kondo semiconductors CeT2Al10 (T=Fe, Ru and Os) possessing a c-f hybridization gap have received considerable attention recently because of the unexpected high magnetic ordering temperature of CeRu2Al10 (TN=27 K) and CeOs2Al10 (TN=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe2Al10 with a paramagnetic ground state down to 50 mK [1-3]. We are investigating this family of compounds, both in polycrystalline and single crystal form, using inelastic neutron scattering to understand the role of anisotropic c-f hybridization on the spin gap formation as well as on their magnetic properties. We have observed a clear sign of a spin gap in all three compounds from our polycrystalline study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our inelastic neutron scattering studies on single crystals of CeRu2Al10 and CeOs2Al10 revealed dispersive gapped spin wave excitations below TN. Analysis of the spin wave spectrum reveals the presence of strong anisotropic exchange, along the c-axis (or z-axis) stronger than in the ab-plane. These anisotropic exchange interactions force the magnetic moment to align along the c-axis, competing with the single ion crystal field anisotropy, which prefers moments along the a-axis. In the paramagnetic state (below 50 K) of the Kondo insulator CeFe2Al10, we have also observed dispersive gapped magnetic excitations which transform into quasi-elastic scattering on heating to 100 K [4-5]. We will discuss the origin of the anisotropic hybridization gap in CeFe2Al10 based on theoretical models of heavy-fermion semiconductors [6-8]. Further the effect of electron- and hole-doping as well as chemical pressure effect on the magnetic and transport properties of CeT2All0 compounds will be discussed. We will compare the observation of spin and charge gap formation in CeT2Al10 with that observed in Ce-based Skutterudite compounds as well as that of topological Kondo insulators.

[1] A. M. Strydom, Physica B 404, 2981 (2009).
[2] Y. Muro et al, Phys. Rev. B 81, 214401 (2010).
[3] D.T. Adroja et al, Physica Scripta, 88, 068505, (2013).
[4] D.T. Adroja et al, Phys Rev. B, 87, 224415 (2013).
[5] J.M. Mignot et al. B 89, 161103(R) (2014).
[6] H. Ikeda and K. Miyake, J. Phys. Soc. Japan, 65, 1796 (1998).
[7] P.S. Riseborough, J. Mag. Mag. Mat. 226-230, 127 (2001).
[8] P.S. Riseborough and S.G.Magalhaes, J. Mag. Mag. Mat. 400, 3 (2016).

Organizer : Satoshi Tsutsui
Mail : satoshi@spring8.or.jp
PHS : 3479

Contact Address SPring-8 Seminar secretariat JASRI/SPring-8 Ayumi Mimura Research Coordination Division
Last modified 2016-07-05 13:16