The quest for materials showing simultaneous ferromagnetism and ferroelectricity at room temperature remains a major challenge. Ferroelectricity and ferromagnetism are usually mutually exclusive, because of their requirement for empty and partially filled transition metal 3d orbitals, respectively. Materials design in a single-phase multiferroic material is keeping as a challenge, although robust magnetoelectric coupling could be achieved by an inverse Dyaloshinski–Moriya (DM) effect in improper ferroelectric systems. However, this usually happens at very low temperature.

In the search for new room-temperature multiferroicity, we have focused on Bi₅Ti₃FeO₁₅ (n = 1, m = 4) (BTFO) which belongs to the class of Aurivillius compounds Bi₄Ti₃O₁₂×nBiMO₃ (M = Fe, Mn; n = 1, 2). Aurivillius compounds with the formula (Bi₂O₂)²⁺(A_m-1B_mO_3m+1)^2- display an amazing variety of both structural and physical properties by changing the A and B cations as well as the number of perovskite-like units (m). BTFO crystallizes in the polar space group A2₁am at room temperature, in which smaller Fe ions are also incorporated into B (Ti) sites, which may cause new magnetically ordered structures. Even so, BTFO has been neither fully characterized nor documented in the multiferroic database for its magnetoelectric coupling performance. Here, we present the first characterization of the magneto-dielectric, magneto-ferroelectric, and ME properties of BTFO thin film. All the evidences point to that Bi₅Ti₃FeO₁₅ is a single-phasemultiferroic material with a robust ME effect at room temperature.

Figure 1. High-angle annular dark-field scanning TEM (HAADF STEM) picture and structure diagram of BTFO film.

*Presenting author’s email: zhy@mail.sic.ac.cn

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