Heat capacity and thermal conductivity of CdCr2Se4 ferromagnet: Magnetic field dependence, experiment and calculations

0573167 - ÚACH 2024 RIV GB eng J - Journal Article
Ahn, K.-H. - Jirák, Z. - Knížek, K. - Levinský, P. - Soroka, Miroslav - Beneš, L. - Zich, J. - Navrátil, J. - Hejtmánek, J.
Heat capacity and thermal conductivity of CdCr2Se4 ferromagnet: Magnetic field dependence, experiment and calculations.
Journal of Physics and Chemistry of Solids. Roč. 174, MAR (2023), č. článku 111139. ISSN 0022-3697. E-ISSN 1879-2553
R&D Projects: GA ČR(CZ) GA19-06433S
Research Infrastructure: e-INFRA CZ - 90140
Institutional support: RVO:61388980
Keywords : CdCr2Se4 * Ferromagnets * Specific heat capacity * Thermal conductivity * Magnons * Phonons
OECD category: Inorganic and nuclear chemistry
Impact factor: 4, year: 2022
Method of publishing: Limited access
https://doi.org/10.1016/j.jpcs.2022.111139

The low-temperature specific heat capacity and thermal conductivity under magnetic field 0-13 T is investigated on polycrystalline sample of the ferromagnetic insulator CdCr2Se4, possessing spinel structure with magnetic Cr3+ ions in the octahedrally coordinated sites. The phonon (lattice) and magnon contributions are separated by their characteristic temperature dependencies and by quenching of the magnon component under high magnetic fields in the isothermal measurements. The results are analyzed with respect to formulas for model systems and confronted with ab-initio calculations of phonon and magnon spectra. The theoretical formula for the fieldinduced quenching of magnon heat capacity is well reproduced, but there are two kinds of deviations from expected behavior deserving attention: (1) Heat capacity at low fields is by several percent lower than expected and approaches the theoretical curve only above0.5 T. We propose that the zero-field magnon heat capacity is diminished by a presence of magnetic domain walls and the expected field dependence is restored when magnetic field converts the sample into a single domain state. (2) The suppression of magnon heat capacity under high magnetic field is incomplete. While the data follow well the theoretical line for given temperature as regards the curvature, the final saturation seems to tend several percent above the expected value for lattice heat capacity. We propose that this behavior is related to the phonon-magnon coupling arising due to Zeeman gap in the magnon spectra and subsequent formation of intersection points with the phonon spectra. The thermal conductivity has shown substantial deviations with respect to model predictions as concerns temperature dependence of the phonon contribution and suppression of the magnon contribution in markedly lower magnetic fields than predicted by the model. We ascribe this discrepancy to a complex character of the intergrain heat transfer.
Permanent Link: https://hdl.handle.net/11104/0343629