Manipulation of Isolated Spins in Ferroelectric Oxides from First Principles

Electric field control of single spins can probe the fundamental atomic-scale limits of multiferroic behavior. One possible platform to explore this scenario is to form isolated spin centers in ferroelectric materials via inclusion of dilute concentrations of magnetic dopants. The preferred orientation of a spin is connected to its local crystallographic environment via the spin-orbit interaction, and is described by the magnetocrystalline anisotropy energy (MCAE). In a ferroelectric material, the local crystallographic environment can be modified by structural changes that occur during polarization switching under applied electric fields, which provides a path towards electric field control of the MCAE and a magnetic dopant’s spin directionality. Although the diverse properties and functionalities of ferroic complex oxides have been the subject of extensive research over the past decades, they have so far received little attention as potential platforms for electric field-based single spin processing, which is of central interest to several modern technological applications. In this work, we combine group theoretic analysis with density functional theory calculations to explore two examples of tuning the spin orientation of isolated magnetic dopant atoms in ferroelectric oxide hosts. We first consider an isolated Fe³⁺ dopant in the tetragonal, orthorhombic, and rhombohedral phases of the prototypical ferroelectric oxide BaTiO₃. We investigate how the MCAE and preferred Fe³⁺ spin orientation evolves as the material traverses these structural phases of different crystalline symmetries, linking these changes to evolution in the electronic structure. Second, we explore an isolated Fe³⁺ dopant in the low-dimensional Aurivillius ferroelectric Bi₂WO₆, tracking how the MCAE and the preferred spin orientation evolve throughout ferroelectric switching. We find that the Fe³⁺ spin aligns along a spin-easy axis in Bi₂WO₆ and that a 90^o switch of the polarization direction leads to a 112^oreorientation of this spin-easy axis. This work advances our understanding of electric field control of single spins, which has potential implications in the fields of spintronics and quantum computing.