Directional dichroism in the paramagnetic state of multiferroics: a case study of infrared light absorption in Sr2CoSi2O7 at high temperatures

Abstract

The coexisting magnetic and ferroelectric orders in multiferroic materials give rise to a handful of novel magnetoelectric phenomena, such as the absorption difference for the opposite propagation directions of light called the non-reciprocal directional dichroism (NDD). Usually these effects are restricted to low temperature, where the multiferroic phase develops. In this paper we report the observation of NDD in the paramagnetic phase of Sr2CoSi2O7 up to temperatures more than ten times higher than its Néel temperature (7 K) and in fields up to 30 T. The magnetically induced polarization and NDD in the disordered paramagnetic phase is readily explained by the single-ion spin-dependent hybridization mechanism, which does not necessitate correlation effects between magnetic ions. The Sr2CoSi2O7 provides an ideal system for a theoretical case study, demonstrating the concept of magnetoelectric spin excitations in a paramagnet via analytical as well as numerical approaches. We applied exact diagonalization of a spin cluster to map out the temperature and field dependence of the spin excitations, as well as symmetry arguments of the single ion and lattice problem to get the spectrum and selection rules.

arXiv comment15 pages, 7 figures

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Cited by in corpus (6)

• Theory for shift current of bosons: Photogalvanic spin current in ferrimagnetic and antiferromagnetic insulators
• Spin excitations of magnetoelectric LiNiPO${}_4$ in multiple magnetic phases
• Magnetic anisotropy and exchange paths for octa- and tetrahedrally coordinated Mn${}^{2+}$ ions in the honeycomb multiferroic Mn${}_2$Mo${}_3$O${}_8$
• Selection rules and dynamic magnetoelectric effect of the spin waves in multiferroic BiFeO${}_3$
• Optical magnetoelectric effect in the polar honeycomb antiferromagnet Fe2Mo3O8
• In-situ electric field control of THz non-reciprocal directional dichroism in the multiferroic Ba${}_2$CoGe${}_2$O${}_7$