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

Abstract

Polarized Raman scattering spectra of the KxCo2-ySe2 (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 KxCo2-ySe2 . 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 B1g mode broadens. We argue that the large asymmetry and anomalous frequency shift of the B1g 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:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Emergent Superconductivity (CES)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1341609
Report Number(s):
BNL-113329-2016-JA
Journal ID: ISSN 0953-8984; R&D Project: PM016; KC0201050; TRN: US1701571
Grant/Contract Number:  
SC0012704; AC02-98CH10886
Resource 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
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Opacic, M., Lazarevic, N., Radonjic, M. M., Scepanovic, M., Ryu, Hyejin, Wang, Aifeng, Tanaskovic, D., Petrovic, C., and Popovic, Z. V. Raman spectroscopy of KxCo2-ySe2 single crystals near the ferromagnet-paramagnet transition. United States: N. p., 2016. Web. doi:10.1088/0953-8984/28/48/485401.
Opacic, M., Lazarevic, N., Radonjic, M. M., Scepanovic, M., Ryu, Hyejin, Wang, Aifeng, Tanaskovic, D., Petrovic, C., & Popovic, Z. V. Raman spectroscopy of KxCo2-ySe2 single crystals near the ferromagnet-paramagnet transition. United States. doi:https://doi.org/10.1088/0953-8984/28/48/485401
Opacic, M., Lazarevic, N., Radonjic, M. M., Scepanovic, M., Ryu, Hyejin, Wang, Aifeng, Tanaskovic, D., Petrovic, C., and Popovic, Z. V. Wed . "Raman spectroscopy of KxCo2-ySe2 single crystals near the ferromagnet-paramagnet transition". United States. doi:https://doi.org/10.1088/0953-8984/28/48/485401. https://www.osti.gov/servlets/purl/1341609.
@article{osti_1341609,
title = {Raman spectroscopy of KxCo2-ySe2 single crystals near the ferromagnet-paramagnet transition},
author = {Opacic, M. and Lazarevic, N. and Radonjic, M. M. and Scepanovic, M. and Ryu, Hyejin and Wang, Aifeng and Tanaskovic, D. and Petrovic, C. and Popovic, Z. V.},
abstractNote = {Polarized Raman scattering spectra of the KxCo2-ySe2 (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 KxCo2-ySe2 . 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 B1g mode broadens. We argue that the large asymmetry and anomalous frequency shift of the B1g 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.},
doi = {10.1088/0953-8984/28/48/485401},
journal = {Journal of Physics. Condensed Matter},
number = 48,
volume = 28,
place = {United States},
year = {2016},
month = {10}
}

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    Works referencing / citing this record:

    Effect of cation-vacancy superstructure on the phonon dynamics in KNi 2 Se 2
    journal, January 2020