Non-d$^0$ Electric Dipole in FeO$_5$ bipyramid: a New Resource for Quantum Paraelectrics, Ferroelectrics and Multiferroics

• Main Authors: Shen, Shi-Peng, Chai, Yi-Sheng, Cong, Jun-Zhuang, Sun, Pei-Jie, Lu, Jun, Yan, Li-Qin, Wang, Shou-Guo, Sun, Young
• Format: Journal Article
• Language: English
• Published: 27.05.2014
• Subjects: Physics - Strongly Correlated Electrons
• DOI: 10.48550/arxiv.1405.6806

Phys. Rev. B 90, 180404(R) (2014) Electric polarization in conventional ferroelectric oxides usually involves nonmagnetic transition-metal ions with an empty d shell (the d$^0$ rule). Here we unravel a new mechanism for local electric dipoles based on magnetic Fe$^{3+}$ (3d$^5$) ion violating the d$^0$ rule. The competition between the long-range Coulomb interaction and short-range Pauli repulsion in a FeO$_5$ bipyramid with proper lattice parameters would favor an off-center displacement of Fe$^{3+}$ that induces a local electric dipole. The manipulation of this kind of non-d$^0$ electric dipoles opens up a new route for generating unconventional dielectrics, ferroelectrics, and multiferroics. As a prototype example, we show that the non-d$^0$ electric dipoles in ferrimagnetic hexaferrites (Ba,Sr)Fe$_{12}$O$_{19}$ lead to a new family of magnetic quantum paraelectrics.