Oral Presentation Crystal36-AXAA Conference 2026

Multiferroic materials are in great focus in modern materials science as they show useful interplay between magnetic and dipole subsystems. New promising multiferroics should have magnetic atoms and polar space group to accommodate spontaneous polarization and magnetic ordering. One such phase, Ca₃Fe₂TiO₈ [1], is structurally intermediate between perovskite CaTiO₃ and brownmillerite Ca₂Fe₂O₅ structures and inherits structural and magnetic properties from both. This compound was previously studied for its thermodynamic and mechanical properties as a cement component. At room temperature its structure can be described by the polar space group Pcm2₁, allowing a spontaneous polarization along the c-axis arising from shifts of tetrahedral FeO₄ units combined with rotations of (Fe/Ti)O₆ the octahedral vertices.

Variable-temperature neutron powder diffraction (NPD) experiments were conducted at ECHIDNA (ANSTO) with two wavelengths of 1.6221 Å and 2.4403 Å. According to the analysis of maximal subgroups the model with P_2Acm2₁ space group was confirmed to best fit the neutron data. This space group restricts tetrahedral iron from having M_y component, while having no restrictions on octahedral positions. The resulting refinement showed mainly the alignment of the magnetic moment with c-axis with slight deviation from it to b-direction on the octahedral sites. The magnetic moment at 3 K were refined to be 3.26(9) and 4.0(1)_B for the tetrahedral and octahedral positions correspondingly. A critical exponent fit points to an ordering temperature around 310 K.

Figure 1. (Left) Refined magnetic moment on Fe-tetrahedral position (blue), Fe-octahedral position (yellow), M_y component of octahedral position (pink);
(Right) Final magnetic structure with magnetic moments on iron atoms, oxygens omitted.