skip to main content

DOE PAGESDOE PAGES

Title: Raman spectroscopy of KxCo2-ySe2 single crystals near the ferromagnet-paramagnet transition

Polarized Raman scattering spectra of the K xCo 2-ySe 2 (x = :::; y = :::) single crystals reveal the presence of two phonon modes, assigned as of the A1g and B1g symmetry. Absence of additional modes excludes the possibility of vacancy ordering, unlike in K xCo 2-ySe 2 . The ferromagnetic (FM) phase transition at Tc 74 K leaves a clear fingerprint on the temperature dependence of the Raman mode energy and linewidth. For T > Tc the temperature dependence looks conventional, driven by the thermal expansion and anharmonicity. The Raman modes are rather broad due to the electron-phonon coupling increased by the disorder and spin fluctuation e ects. In the FM phase the phonon frequency of both modes increases, while an opposite trend is seen in their linewidth: the A1g mode narrows in the FM phase, whereas the B 1g mode broadens. We argue that the large asymmetry and anomalous frequency shift of the B 1g mode is due to the coupling of spin fluctuations and vibration. Our density functional theory (DFT) calculations for the phonon frequencies agree rather well with the Raman measurements, with some discrepancy being expected since the DFT calculations neglect the spin fluctuations.
Authors:
 [1] ;  [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [1] ;  [3] ;  [1]
  1. Univ. of Belgrade (Serbia)
  2. Univ. of Augsburg (Germany); Univ. of Belgrade (Serbia)
  3. Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., NY (United States)
  4. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
Report Number(s):
BNL-113329-2016-JA
Journal ID: ISSN 0953-8984; R&D Project: PM016; KC0201050; TRN: US1701571
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
Journal of Physics. Condensed Matter
Additional Journal Information:
Journal Volume: 28; Journal Issue: 48; Journal ID: ISSN 0953-8984
Publisher:
IOP Publishing
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
OSTI Identifier:
1341609