Metallic ferroelectric-ferromagnetic multiferroics in strained EuTi O3-x Hx


Polar metals are defined by the coexistence of metallicity and polar crystal structure. They have potential applications in nonlinear optics, ferroelectric devices, and quantum devices. Meanwhile, ferroelectric-ferromagnetic (FE-FM) multiferroics display simultaneous ferroelectricity and ferromagnetism, leading to new technologies in information storage. It is exceedingly scarce that metallicity, ferroelectricity, and ferromagnetism can coexist simultaneously in a material. Here, using the results from hybrid density-functional theory calculations, we report metallic FE-FM multiferroics in strain-engineered epitaxial EuTiO3 with H doping. The emergence of the magnetism in polar metals provides a degree of freedom to control these materials in applications. The underlying mechanism for the coexistence of metallicity, ferroelectricity, and ferromagnetism is discussed. The ferromagnetism in metallic EuTiO3-xHx is explained by the Ruderman-Kittel-Kasuya-Yosida interaction, which agrees with experiments. The coexistence of metallicity and ferroelectricity is allowed because the electrons at the Fermi level are weakly coupled to the ferroelectric distortion. Our results suggest that the combined effect of strain and doping is responsible for achieving EuTiO3-based metallic multiferroics and may provide a way for obtaining metallic multiferroics in other materials.

Publication Title

Physical Review B