Soft antiphase tilt of oxygen octahedra in the hybrid improper multiferroic Ca3Mn1.9Ti0.1O7

TL;DR

This study investigates the structural and magnetic properties of Ca3Mn1.9Ti0.1O7, revealing the temperature and pressure dependence of antiphase tilt and its relation to multiferroic behavior.

Contribution

It provides detailed insights into the soft antiphase tilt behavior and its influence on multiferroicity in Ca3Mn1.9Ti0.1O7, a prototypical hybrid improper multiferroic.

Findings

Antiphase tilt decreases with temperature and pressure.

In-plane rotation remains stable across transitions.

Canted ferromagnetic moment is minimal despite octahedral tilt.

Abstract

We report a single crystal neutron and x-ray diffraction study of the hybrid improper multiferroic Ca3Mn1.9Ti0.1O7 (CMTO), a prototypical system where the electric polarization arises from the condensation of two lattice distortion modes.With increasing temperature (T ), the out-of-plane, antiphase tilt of MnO6 decreases in amplitude while the in-plane, in-phase rotation remains robust and experiences abrupt changes across the first-order structural transition. Application of hydrostatic pressure (P) to CMTO at room temperature shows a similar effect. The consistent behavior under both T and P reveals the softness of antiphase tilt and highlights the role of the partially occupied d orbital of the transition-metal ions in determining the stability of the octahedral distortion. Polarized neutron analysis indicates the symmetry-allowed canted ferromagnetic moment is less than the 0.04 {\mu}B/Mn site, despite a substantial out-of-plane tilt of the MnO6 octahedra.