Coupled spin-lattice fluctuations in a compound with orbital degrees of freedom: The Cr-based dimer system Sr3Cr2O8

Abstract

We report on an extended fluctuation regime in the spin dimer system Sr3Cr2O8 based on anomalies in Raman active phonons and magnetic scattering. The compound has two characteristic temperatures, TS = 275 K, related to a Jahn-Teller transition with structural distortions and orbital ordering and a second, T * ≈ 150 K, which is due to further changes in the orbital sector. Below TS quasielastic scattering marks strong fluctuations and in addition phonon anomalies are observed. For temperatures below T * we observe an exponential decrease of one phonon linewidth and determine a gap of the orbital excitations. At low temperatures the observation of two-and three-magnon scattering allows the determination of the spin excitation gap.

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. BSelf Cite1000View full textAdd to dashboardCite

“…2(b)]. For the mixed compounds x = 2.9 and x = 2.8, the Jahn-Teller transition temperatures are T J T = 260 K and 242 K, whereas for the pure Sr 3 Cr 2 O 8 T J T is 285 K and 70 K for Ba 3 Cr 2 O 8 , respectively [12,13].…”

“…This indicates a possible mixing of the orbital excitation and a phonon. A factor group analysis [13] gives the number of Raman active phonons that was analyzed for the parent compound Sr 3 Cr 2 O 8 . 11 Raman active phonon modes are expected in the hexagonal symmetry R3m and 39 corresponding modes in the monoclinic space group C2/c out of which only 26 modes were observed.…”

“…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.…”

“…Raman scattering investigations performed on a single crystal of Sr 3 Cr 2 O 8 have found that new phonons, linked to the C2/c space group, are not emerging right below the Jahn-Teller transition, but instead there is an extended temperature regime where the lattice is fluctuating [13]. This lattice fluctuation regime was linked to orbital ordering and further changes in the orbital sector below the Jahn-Teller transition temperature T J T [8].…”