Density Functional Investigation of the Antiferromagnetic Ordering, Spin Orientation, and Ferroelectric Polarization of Rare-Earth IronBorate TbFe3(BO3)4

摘要

First-principles density functional calculations were carried out to examine the electronic and magnetic properties of rare-earth iron borate TbFe3(BO3)4. The spin exchange interactions between the Fe~(3+) (d~5, S = 5/2) ions and the preferred orientation of the Tb~(3+) (f~8) spins were evaluated, and the ferroelectric polarization of TbFe3(BO3)4 was calculated. In agreement with experiment, our calculations predict that the spin exchange between the Fe~(3+) spins is ferromagnetic within each //ab sheet of Fe~(3+) ions but antiferromagnetic between adjacent //ab sheets of Fe~(3+) ions, whereas the spin exchange between the Fe~(3+) and Tb~(3+) ions within each //ab sheet of Fe~(3+) and Tb~(3+) ions is antiferromagnetic. The Tb~(3+) (f~8) ions is found to possess an electron configuration responsible for uniaxial magnetism, hence orienting the Tb~(3+) spins along the c-direction and leading to the highly anisotropic magnetic susceptibility. The ferroelectric polarization of TbFe3(BO3)4 is largely due to the absence of inversion symmetry of the crystal structure and is weakly affected by its magnetic structure.