Abstract
The magnetic specific heat of and the spin state of ions in the compound have been studied. Phonon dispersion and phonon density of states (PDOS), element specific and total, were evaluated from first-principles calculations. It is shown that iron atoms in quasi-one-dimensional chains have dramatically different vibrational properties against Rb and Se atoms: the Fe PDOS is mostly concentrated within two Einstein-like optical phonon peaks at high frequencies. Analysis of our Mössbauer data for , utilizing the calculated Fe PDOS as well as our optical absorption measurements, have shown full agreement with the location of the high-frequency optical-type lattice vibrations within the tetrahedra. The calculated PDOS was utilized to evaluate the lattice contribution to the specific heat. The phonon heat capacity has been used to evaluate the magnetic specific heat of the quasi-one-dimensional antiferromagnetically correlated ion chains in . An intermediate spin state has been found most closely relevant to our magnetic entropy analysis for ions in .
- Received 3 September 2018
- Revised 9 November 2018
DOI:https://doi.org/10.1103/PhysRevB.98.214411
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