Abstract-Terahertz spin-orbital excitations in the paramagnetic state of multiferroic Sr2FeSi2O7

Thuc T. Mai, C. Svoboda, M. T. Warren, T.-H. Jang, J. Brangham, Y. H. Jeong, S.-W. Cheong, and R. Valdés Aguilar

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.224416

We studied the novel multiferroic material Sr2FeSi2O7 and found three absorption modes above the magnetic ordering transition temperature using time-domain terahertz spectroscopy. These absorption modes can be explained as the optical transitions between the spin-orbit coupling and crystal-field split 3d6Fe2+ ground-state term in this material. Consideration of the compressed tetrahedral environment of the Fe2+ site is crucial to understand the excitations. We point out, however, discrepancies between the single-site atomic picture and the experimental results.

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Abstract-Terahertz spectroscopy of spin waves in multiferroic BiFeO3 in high magnetic fields

U. Nagel, Randy S. Fishman, T. Katuwal, H. Engelkamp, D. Talbayev, Hee Taek Yi, S.-W. Cheong, and T. Rõõm

http://prl.aps.org/accepted/51074YbaOc61af34479852839f520a457f017897b

We have studied the magnetic field dependence of far-infrared active magnetic modes in a single ferroelectric domain \BFO/ crystal at low temperature. The modes soften close to the critical field of 18.8\,T along the [001] (pseudocubic) axis, where the cycloidal structure changes to the homogeneous canted antiferromagnetic state and a new strong mode with linear field dependence appears that persists at least up to 31\,T. A microscopic model that includes two \DM/ interactions and easy-axis anisotropy describes closely both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. The good agreement of theory with experiment suggests that the proposed model provides the foundation for future technological applications of this multiferroic material.