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![]() TSURKAN, Vladimir, ZAHARKO, Oksana, SCHRETTLE, Florian, KANT, Ch., DEISENHOFER, Joachim, KRUG VON NIDDA, Hans Albrecht, FELEA, Viorel, LEMMENS, Peter, GROZA, Joanna R., QUACH, Dat V., GOZZO, Fabia, LOIDL, Alois. Structural anomalies and the orbital ground state in FeCr2S 4. In: Physical Review B - Condensed Matter and Materials Physics, 2010, vol. 81, p. 0. ISSN 1098-0121. DOI: https://doi.org/10.1103/PhysRevB.81.184426 |
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Physical Review B - Condensed Matter and Materials Physics | |
Volumul 81 / 2010 / ISSN 1098-0121 /ISSNe 1550-235X | |
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DOI:https://doi.org/10.1103/PhysRevB.81.184426 | |
Pag. 0-0 | |
Rezumat | |
We report on high-resolution x-ray synchrotron powder-diffraction, magnetic-susceptibility, sound-velocity, thermal-expansion, and heat-capacity studies of the stoichiometric spinel FeCr2S4. We provide clear experimental evidence of a structural anomaly which accompanies an orbital-order transition at low temperatures due to a static cooperative Jahn-Teller effect. At 9 K, magnetic susceptibility, ultrasound velocity, and specific heat reveal pronounced anomalies that correlate with a volume contraction as evidenced by thermal-expansion data. The analysis of the low-temperature heat capacity using a mean-field model with a temperature-dependent gap yields a gap value of about 18 K and is interpreted as the splitting of the electronic ground state of Fe2+ by a cooperative Jahn-Teller effect. This value is close to the splitting of the ground state due to spin-orbit coupling for isolated Fe2+ ions in an insulating matrix, indicating that Jahn-Teller and spin-orbit coupling are competing energy scales in this system. We argue that due to this competition, the spin-reorientation transition at around 60 K marks the onset of short-range orbital ordering accompanied by a clear broadening of Bragg reflections, an enhanced volume contraction compared to usual anharmonic behavior, and a softening of the lattice observed in the ultrasound measurements. |
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Cuvinte-cheie magnetism, Curie Temperature, Antiferromagnet |
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