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  Magnetic field induced softening of spin waves and hard-axis order in the Kondo-lattice ferromagnet CeAgSb2

Nikitin, S. E., Podlesnyak, A., Xu, J., Voneshen, D., Le, M. D., Bud'ko, S. L., et al. (2021). Magnetic field induced softening of spin waves and hard-axis order in the Kondo-lattice ferromagnet CeAgSb2. Physical Review B, 104(11): 115169, pp. 1-12. doi:10.1103/PhysRevB.104.115169.

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 Creators:
Nikitin, S. E.1, Author              
Podlesnyak, A.2, Author
Xu, J.2, Author
Voneshen, D.2, Author
Le, Manh Duc2, Author
Bud'ko, S. L.2, Author
Canfield, P. C.2, Author
Sokolov, D. A.1, Author              
Affiliations:
1Physics of Quantum Materials, Max Planck Institute for Chemical Physics of Solids, Max Planck Society, ou_1863462              
2External Organizations, ou_persistent22              

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 Abstract: A significant number of Kondo-lattice ferromagnets order perpendicular to the easy magnetization axis dictated by the crystalline electric field. The nature of this phenomenon has attracted considerable attention, but remains poorly understood. In the present paper we use inelastic neutron scattering supported by magnetization and specific heat measurements to study the spin dynamics in the hard-axis ferromagnet CeAgSb2. In the zero-field state we observed two sharp magnon modes, which are associated with Ce ordering and extended up to approximate to 3 meV with a considerable spin gap of 0.6 meV. Application of a magnetic field perpendicular to the moment direction reduces the spectral intensity and suppresses the gap and significantly enhances the low-temperature specific heat at a critical field of B-c approximate to 2.8 T via a mean-field-like transition. Above the transition, in the field-polarized state, the gap eventually reopens due to the Zeeman effect. We modeled the observed dispersion using linear spin-wave theory taking into account the ground-state Gamma(6) doublet and exchange anisotropy. Our model correctly captures the essential features of the spin dynamics including magnetic dispersion, distribution of the spectral intensity, as well as the field-induced behavior, although several minor features remain obscure. The observed spectra do not show significant broadening due to the finite lifetime of the quasiparticles. Along with a moderate electronic specific heat coefficient gamma = 46 mJ/mol K-2 this indicates that the Kondo coupling is relatively weak and the Ce moments are well localized. Altogether, our results provide profound insight into the spin dynamics of the hard-axis ferromagnet CeAgSb2 and can be used as solid ground for studying magnetic interactions in isostructural compounds including CeAuSb2, which exhibits nematicity and unusual mesoscale magnetic textures.

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Language(s): eng - English
 Dates: 2021-09-302021-09-30
 Publication Status: Published in print
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Title: Physical Review B
  Abbreviation : Phys. Rev. B
Source Genre: Journal
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Publ. Info: Woodbury, NY : American Physical Society
Pages: - Volume / Issue: 104 (11) Sequence Number: 115169 Start / End Page: 1 - 12 Identifier: ISSN: 1098-0121
CoNE: https://pure.mpg.de/cone/journals/resource/954925225008