Multiferroicity and magnetoelectric effects in two-dimensional materials
The recent discovery of magnetic two-dimensional (2D) van der Waals materials opened a myriad of new possibilities in the field of spintronics regarding the control and manipulation of their magnetic order. There are also 2D materials characterized by different types of ferroic order: ferroelectricity or ferroelasticity, which respond to electric and stress fields, respectively. In a small subset of materials two distinct types of order can be found, even simultaneously, giving rise to the so-called multiferroics. These multifunctional materials display unique properties due to their cross-couplings between ferroic orders; magnetoelectric effect, magnetoelastic and piezoelastic interactions. However, 2D multiferroics are rare and I will discuss the conditions and mechanisms of their formation. Furthermore, I will analyze the interplay between the magnetic and ferroelectric orders in selected 2D materials and their dependence on doping, strain, and electric field, based on first-principles density-functional-theory calculations. Understanding the coexisting orders can help in discovering new multifunctional materials and suggest new ways of spin-current manipulation.