Abstract
We present results of a multimethod investigation of the polar antiferromagnets and , inspired by the colossal magnetoelectric effect present in . Both compounds crystalize in the same polar space group as , preserving the crystal symmetry at least from room temperature down to 2 K. and undergo antiferromagnetic phase transitions at and 52 K, and spin-flop transitions at an external magnetic field of approximately 8 and 4 T, respectively. Both compounds present an incommensurate antiferromagnetic helical structure with spins lying in the plane, in contrast to the collinear one along the axis in . Moreover, dielectric anomalies are observed at their antiferromagnetic phase transitions, suggesting a magnetoelectric behavior. Spin and lattice dynamics studies by a combination of infrared, Raman, and terahertz spectroscopies were performed. Below , in both and , low-frequency spin excitations extremely sensitive to external magnetic field were observed. At least one of these magnons was simultaneously seen in Raman and THz spectra of both compounds, therefore we propose to assign them to electromagnons.
- Received 10 September 2019
DOI:https://doi.org/10.1103/PhysRevB.101.014429
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