Unidirectional terahertz light absorption in the pyroelectric ferrimagnet CaBaCo4O7

Bordács, Sándor and Kocsis, Vilmos and Tokunaga, Yusuke and Nagel, Urmas and Rõõm, Toomas and Takahashi, Youtarou and Taguchi, Yasujiro and Tokura, Yoshinori (2015) Unidirectional terahertz light absorption in the pyroelectric ferrimagnet CaBaCo4O7. PHYSICAL REVIEW B CONDENSED MATTER AND MATERIALS PHYSICS, 92 (21). No. 214441. ISSN 1098-0121

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Abstract

Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which is a type-I multiferroic compound with the largest magnetic-order induced ferroelectric polarization (ΔP=17 mC/m2) reported, so far. We observed two optical magnon branches: a solely electric dipole allowed one and a mixed magnetoelectric resonance. The entangled magnetization and polarization dynamics of the magnetoelectric resonance gives rise to unidirectional light absorption, i.e., that magnon mode absorbs the electromagnetic radiation for one propagation direction but not for the opposite direction. Our systematic study of the magnetic field and temperature dependence of magnon modes provides information about the energies and symmetries of spin excitations, which is required to develop a microscopic spin model of CaBaCo4O7.

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