Mechanism for strong magnetoelectric coupling in dilute magnetic ferroelectrics

Abstract

The manipulation of atomic-scale magnetization is important from both a fundamental and a practical perspective. Using first-principles density-functional-theory calculations within the hybrid functional approach, we systematically study spin-lattice coupling effects for isolated $3{d}^{4}--3{d}^{7}$ transition-metal dopants in a nonmagnetic, ferroelectric ${\mathrm{PbTiO}}_{3}$ host material. When present at the B-site, a low-spin (or intermediate-spin) to high-spin crossover induces marked ferroelectric-like distortions in the local geometry, characterized by a shift of the dopant ion with respect to the surrounding ${\mathrm{O}}_{6}$ octahedral cage. The origins of this microscopic multiferroic effect are discussed in terms of the pseudo-Jahn-Teller theory for ferroelectricity. The possibility to exploit this phenomenon to achieve strong magnetoelectric coupling, including controlled spin switching, is also investigated. These results provide a further understanding of ferroelectricity and multiferroicity in perovskite oxides, and they suggest a possible pathway to manipulate single atomic spins in semiconductor solid solutions.