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MA: Fachverband Magnetismus

MA 15: Magnetism Poster A

MA 15.65: Poster

Dienstag, 2. April 2019, 10:00–13:00, Poster E

Spin reduction in covalent chain antiferromagnet RbFeSe₂ — •Hans-Albrecht Krug von Nidda¹, Airat Kiiamov², Lenar Tagirov^2,3, Yury Lysogorsky^2,5, Dmitrii Tayurskii², Zakir Seidov¹, Vladimir Tsurkan^1,4, Dorina Croitori⁴, Axel Günther¹, Farit Vagizov², Franz Mayr¹, and Alois Loidl¹ — ¹EP V, EKM, University of Augsburg, D-86135 Augsburg — ²Institute of Physics, Kazan Federal University, RUS-420008 Kazan — ³Zavoisky Physical-Technical Institute, Kazan FRC of RAS, 420029 Kazan — ⁴Institute of Applied Physics, MD-20208 Chisinau — ⁵ICAMS, Ruhr-University Bochum, D-44801 Bochum

SQUID susceptibility, Mössbauer and specific-heat measurements show that RbFeSe₂ exhibits antiferromagnetic order below T_N=248 K. The magnetic specific heat of RbFeSe₂ and the spin state of Fe³⁺ ions in the compound have been analyzed. Phonon dispersion and PDOS, 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. Analysis of our Mössbauer data, 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 FeSe₄ tetrahedra. The phonon heat capacity has been used to evaluate the magnetic specific heat of the quasi 1D antiferromagnetically correlated Fe³⁺ ion chains. The magnetic entropy suggests an intermediate spin state S=3/2 for Fe³⁺ ions in agreement with the reduced hyperfine field of 216 kOe at 4.2 K detected by Mössbauer spectroscopy.