Unconventional spin-phonon coupling via the Dzyaloshinskii???Moriya interaction

Spin-phonon coupling (SPC) plays a critical role in numerous intriguing phenomena of transition metal oxides (TMOs). In 3d and 4d TMOs, the coupling between spin and lattice degrees of freedom is known to originate from the exchange interaction. On the other hand, the origin of SPC in 5d TMOs remains to be elucidated. To address this issue, we measured the phonon spectra of the 5d pyrochlore iridate Y 2 Ir 2 O 7 using optical spectroscopy. Three infrared-active phonons soften below the N??el temperature of T N ??? 170 K, indicating the existence of strong SPC. Simulations using density functional theory showed that the coupling is closely related to the Ir???O???Ir bond angle. A tight-binding model analysis reveals that this SPC is mainly mediated by the Dzyaloshinskii???Moriya interaction rather than the usual exchange interaction. We suggest that such unconventional SPC may be realized in other 5d TMOs with non-collinear magnetic order

Strong Spin-Phonon Coupling Mediated by Single Ion Anisotropy in the All-In-All-Out Pyrochlore Magnet Cd2Os2 O7

Spin-phonon coupling mediated by single ion anisotropy was investigated using optical spectroscopy and first-principles calculations in the all-in-all-out pyrochlore magnet Cd2Os2O7. Clear anomalies were observed in both the phonon frequencies and linewidths at the magnetic ordering temperature. The renormalization of the phonon modes was exceptionally large, signifying the presence of an unconventional magnetoelastic term from large spin-orbit coupling. In addition, the relative phonon frequency shifts show a strong correlation with the modulation of noncubic crystal field by the corresponding lattice distortion. Our observation establishes a new type of spin-phonon coupling through single ion anisotropy, a second-order spin-orbit coupling term, in Cd2Os2O7. © 2017 American Physical Society4

Spin-orbit coupling induced band structure change and orbital character of epitaxial IrO2 films

We investigated the electronic structure of IrO2 to address the controversy regarding spin-orbit coupling (SOC) effects in metallic 5d transition-metal oxides. Two issues have come to the forefront: (1) SOC effects on electronic structure and physical properties of IrO2 and (2) the possible formation of a novel ground state in this material, the J(eff) = 1/2 state. To better understand the SOC mechanism, we grew epitaxial IrO2 films whose dc resistivity values were comparable with those of a single crystal. We obtained polarization-dependent optical and x-ray absorption spectra (XAS) and compared these results with those acquired using the generalized gradient approximation (GGA) and GGA + SOC calculations. From the optical spectra, peak structures were identified at 0.4 and 2.0 eV, which could only be explained using the GGA + SOC calculation. This suggests that SOC plays an important role in the electronic structure of IrO2. From the polarization-dependent O 1s XAS spectra, we observed that the empty state near the Fermi level lacks involvement of an Ir d(xy) orbital. Despite the importance of SOC in IrO2, the J(eff) = 1/2 state does not form in metallic IrO2