Single-crystallineBiMnO3studied by temperature-dependent x-ray diffraction and Raman spectroscopy

Abstract

We report on the temperature dependence of the phonons and crystallographic parameters in BiMnO 3 single crystals grown under high pressure and high temperature. The crystallographic structure of the sample was refined from room temperature to liquid helium temperature in the centrosymmetric C2/c space group, i.e., a group which does not allow ferroelectricity. In addition, the lattice dynamics was probed by Raman spectroscopy down to liquid nitrogen temperature, i.e., below the ferromagnetic transition at T C = 100 ± 2 K. Both crystallographic and Raman data indicate the absence of a structural phase transition at the ferromagnetic ordering or any other temperature. The Raman signature around T C shows a significant spin-phonon coupling for the high-frequency bands.

Spin–phonon coupling in monoclinic BiCrO3

“…where ( ) is the average magnetization per magnetic ion at temperature , and 0 is the saturated magnetization. Such a model works well for different perovskites even in a system with antisymmetric phonon renormalizations, 36,47,48 which could be the case of BCO. Figure 6 shows Δ as a function of ( ( )/ 0 ) 2 as related by the equation (5).…”

Optical study of the vibrational and dielectric properties ofBiMnO3

“…In Ref. 22, a low-frequency shift was reported for the Raman bands at 513.8 cm −1 and 637.4 cm −1 below T c . The authors attribute this observation to a spin-phonon coupling which is switched on by the FM transition.…”

“…Given the weak Tdependence observed in both spectra (see Table I and Ref. 22) the best resolved IR spectrum has been chosen for a more meningful comparison. ferred spectral weight comes from, presumably the electronic bands in the visible and the UV, which are out of the present measuring range.…”

“…The experiment was done at room temperature, considering that diffraction data exclude phase transitions below 300 K [23], and that neither the Raman lines in Ref. 22, nor the infrared modes in Table I Table I. 7500 12 18 426 56000 34 421 40000 46 19 463 80000 28 462 39000 30 20 486 110000 35 489 60000 45 21 508 48000 38 22 541 47000 22 545 46000 25 23 561 125000 35 565 122000 39 24 604 3000 46 25 628 18000 26 629 10000 28 major frequency shifts down to the lowest temperatures.…”

Elaboration and Characterization of Materials from the LaMnO3–BiMnO3 Binary System

“…Indeed, BiMnO 3 can only be obtained by high‐pressure synthesis: BiMnO 3 perovskite compound decomposes around 600 °C into Bi 2 O 3 and Bi 2 Mn 4 O 9 . BiMnO 3 is an insulating ferromagnetic compound at low temperature ( T C = 102 K) and presents at room temperature a monoclinic structure with space group C2/c …”