Magnetic field induced softening of spin waves and hard-axis order in the Kondo-lattice ferromagnet CeAgSb 2

Nikitin, S. E.; Podlesnyak, A.; Xu, J.; Voneshen, D.; Le, Manh Duc; Bud'ko, S. L.; Canfield, P. C.; Sokolov, D. A.

doi:10.1103/PhysRevB.104.115169

Title: Magnetic field induced softening of spin waves and hard-axis order in the Kondo-lattice ferromagnet ${CeAgSb}_{2}$

Journal Article · Thu Sep 30 00:00:00 EDT 2021 · Physical Review B

DOI:https://doi.org/10.1103/PhysRevB.104.115169· OSTI ID:1823197

Nikitin, S. E.;

; Xu, J.; Voneshen, D.;

; Bud'ko, S. L.; Canfield, P. C.; Sokolov, D. A.

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 ≈ 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 ≈ 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 Γ₆ 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 γ = 46 mJ/mol K² 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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Research Organization:: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Ames Laboratory (AMES), Ames, IA (United States)

Sponsoring Organization:: USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division

Grant/Contract Number:: AC02-07CH11358; AC05-00OR22725

OSTI ID:: 1823197

Alternate ID(s):: OSTI ID: 1826008; OSTI ID: 1827099

Report Number(s):: IS-J-10,606; PRBMDO; 115169

Journal Information:: Physical Review B, Journal Name: Physical Review B Vol. 104 Journal Issue: 11; ISSN 2469-9950

Publisher:: American Physical SocietyCopyright Statement

Country of Publication:: United States

Language:: English

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Title: Magnetic field induced softening of spin waves and hard-axis order in the Kondo-lattice ferromagnet CeAgSb 2

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Title: Magnetic field induced softening of spin waves and hard-axis order in the Kondo-lattice ferromagnet ${CeAgSb}_{2}$