Infrared phonons and specific heat in the gapped quantum magnet Ba3Cr2O8

Abstract

We report on the phonon spectrum of the spin-gapped quantum magnet Ba3Cr2O8 determined by infrared spectroscopy, and on specific heat measurements across the Jahn-Teller transition in magnetic fields up to 9 T. Phonon modes split below the Jahn-Teller transition, which occurs at TJT = 70 K as detected by specific-heat measurements. The field-dependent specific heat data is analyzed in terms of the contributions from lattice, magnetic and orbital degrees of freedom. In contrast to the isostructural compound Sr3Cr2O8 our analysis does not indicate the existence of orbital fluctuations below the Jahn-Teller transition in Ba3Cr2O8.

FeCr2S4 in magnetic fields: possible evidence for a multiferroic ground state

“…in KCuF 3 and LaMnO 3 . [4][5][6] Similar electronic configurations are found in the case of compounds containing Fe 2+ or Cr 3+ -ions in a tetrahedral crystal-field, [2,[7][8][9][10] but the electron-lattice coupling is generally weaker and competes with spin-orbit coupling and exchange interactions, leading to strong fluctuations and frustration effects. FeCr 2 S 4 is a sulfur spinel that has been reported previously to exhibit a complex interplay of orbital correlations and magnetism, including ferrimagnetic ordering of the Cr and Fe sublattices below T C ≈ 170 K [11,12] and a transition at T OO = 10 K, which has been assigned to originate from orbital ordering.…”

Tuning the orbital-lattice fluctuations in the mixed spin-dimer system Ba3−xSrxCr2O8Gazizulina1, Quintero-Castro2, Wulferding3 et al. 2018Phys. Rev. B1000View full textAdd to dashboardCite

“…The dimers are antiferromagnetically linked in a triangular in-plane arrangement, resulting in a certain degree of magnetic frustration. A Jahn-Teller transition is reported at temperatures T J T = 285 K for Sr 3 Cr 2 O 8 [8] and T J T = 70 K for Ba 3 Cr 2 O 8 [9]. The Jahn Teller transition is related to a structural transition from trigonal R3m to monoclinic C2/c appearing in both compounds ( Fig.…”

“…These fluctuations are reduced with decreasing temperature and all the modes of the monoclinic structure are observed when the temperature is lower than T * . This is not the case for Ba 3 Cr 2 O 8 where there is no sign of orbital fluctuations below T J T [9].…”

“…The differences in the dynamic lattice-orbital properties between these two systems stand in contrast to their magnetic ground state (singlet) and magnetic excitations (triplons) which are essentially similar in both compounds [11,12,14]. [9,[11][12][13]. J 0 and J e are intradimer and interdimer magnetic exchange interactions, receptively.…”

“…Multiple parameters contribute to the heat capacity in this compound, the orbital gap between the d 3z 2 −r 2 and d x 2 −y 2 , the spin gap, the lattice contribution, and the Jahn-Teller transition anomaly. Analysis of the heat capacity in Sr 3 Cr 2 O 8 [8], together with ESR data [14], allowed us to extract an orbital gap of 388 K and a spin gap of 27 K. On the other hand, measurements of the heat capacity in Ba 3 Cr 2 O 8 have allowed us to determine corresponding entropy which reaches a value slightly lower than expected [9]. An important difference between these compounds is that Ba 3 Cr 2 O 8 recovers all the orbital entropy after the Jahn Teller transition, whereas Sr 3 Cr 2 O 8 exceeds that entropy reaching a value slightly higher than expected [8].…”