"Magnetoelectric properties in antiferromagnets composed of square cupolas", Yasuyuki Kato (U Tokyo)

• Speaker: Yasuyuki Kato (Univ. Tokyo)
• Date: October 3rd (Tue)
• Time: 14:00-15:00
• Venue: D015, Lab1

Title: Magnetoelectric properties in antiferromagnets composed of square cupolas

Abstract:

Magnetoelectric (ME) effect is cross correlations between dielectricity and magnetism such as the direction of magnetic pole is controlled by the electric field. In ME active compounds, the spin degrees of freedom (origin of magnetic moment) play an important role for the cross correlation. A variety of mechanisms connecting the spin degrees of freedom and the electric dipole have been confirmed, and the ME responses specific to the low temperature magnetic order have been observed in various compounds.

We study the ME properties in a newly synthesized quasi-two-dimensional magnets Ba(TiO)Cu₄(PO₄)₄ by a combined experimental and theoretical study of a quasi-two-dimensional magnetodielectric material. The important building block of these compounds is Cu₄O₁₂ forming antiferromagnetic square cupolas where the local inversion symmetry is absent. The loss of inversion symmetry activates the asymmetric interactions between spins through the relativistic spin-orbit coupling. Such interactions can lead to intriguing magnetism, e.g., weak ferromagnetism in antiferromagnets and spin-spiral ordering in helimagnets. We experimentally obtain the magnetization curve up to above the saturation field, and several anomalies are observed depending on the magnetic field directions. We propose a quantum spin model, which well reproduces the full magnetization curves. Elaborating the phase diagram of the model, we show that the anomalies are explained by magnetoelectric phase transitions. Our theory also accounts for the scaling of the dielectric anomaly observed in experiments.

Reference: Y. Kato, et. al., Phys. Rev. Lett. 118, 107601 (2017).