Local inversion symmetry breaking and spin-phonon coupling in the perovskite GdCrO3

Abstract

Our detailed temperature dependent synchrotron powder x-ray diffraction studies along with first-principles density functional perturbation theory calculations, enable us to shed light on the origin of ferroelectricity in GdCrO3. The actual lattice symmetry is found to be noncentrosymmetric orthorhombic P na21 structure, supporting polar nature of the system. Polar distortion is driven by local symmetry breaking and by local distortions dominated by Gd off-centering. Our study reveals an intimate analogy between GdCrO3 and YCrO3. However, a distinctive difference exists that Gd is less displacive compared to Y, which results in an orthorhombic P na21 structure in GdCrO3 in contrast to monoclinic structure in YCrO3 and consequently, decreases its polar property. This is due to the subtle forces involving Gd-4f electrons either directly or indirectly. A strong magneto-electric coupling is revealed using Raman measurements based analysis in the system below Cr-ordering temperature, indicating their relevance to ferroelectric modulation.

Spin–phonon coupling in monoclinic BiCrO3

“…In this study, the authors observed similar spin-phonon coupling effects confirmed through the FHWM analysis in samples where the R 3+ site is occupied by magnetic ions. Also, Mahana et al 36 recently reported the spin-phonon coupling of GdCrO3 in which the phonon frequencies also presented a mix of hardening and softening effects below TN, as observed in our BCO study. In both cases, the magnitude of the reported renormalizations was in the order of 1 -3 cm -1 in good accordance with those observed here.…”

“…Once the FWHM is related to the phonon lifetime, 35 it is not affected by anomalous thermal lattice variations. Thus, the analysis of the FWHM behavior is an important tool to distinguish between events related to subtle volume changes due to exchange-striction 36 or magnetostriction and phenomena related to coupling effects. 37 In this way, the FWHM for all selected modes also presented subtle renormalizations at 110 and 80 K indicating the presence of a sin-phonon coupling at these temperatures.…”

“…In general, besides the magnetic order, depends on how the phonon modulates the exchange interaction. 36,41 This is the author's peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.…”

Temperature dependent X‐ray diffraction and Raman spectroscopy studies of polycrystalline YCrO3 ceramics across the TC ~ 460 K

“…Hence, we choose YCO to study the competitive role of octahedral rotation and A‐cationic displacement to find the origin of suppression of ferroelectricity in this system. More recently, Mahana et al have shown similar polar distortion of Gd 3+ off‐centering driven by local symmetry breaking in orthorhombic Pna2 1 structure of GdCrO 3 analogous to YCO . However, both these studies have concluded the local non‐centrosymmetricity based on bulk measurement techniques such as powder neutron or X‐ray diffraction (XRD) only.…”

“…More recently, Mahana et al have shown similar polar distortion of Gd 3+ off-centering driven by local symmetry breaking in orthorhombic Pna2 1 structure of GdCrO 3 analogous to YCO. [17] However, both these studies have concluded the local non-centrosymmetricity based on bulk measurement techniques such as powder neutron or X-ray diffraction (XRD) only. Raman spectroscopy being a local probe can provide a better insight to enquire the local distortion compared with neutron or XRD.…”