Multiple polarization phases and strong magnetoelectric coupling in the layered transition metal phosphorus chalcogenides <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>T</mml:mi><mml:mi>M</mml:mi><mml:msub><mml:mi mathvariant="normal">P</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>X</mml:mi><mml:mn>6</mml:mn></mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mi>T</mml:mi><mml:mo>=</mml:mo><mml:mi>Cu</mml:mi><mml:mo>,</mml:mo><mml:mspace width="0.16em"/><mml:mi>Ag</mml:mi><mml:mo>;</mml:mo><mml:mspace width="0.16em"/><mml:mi>M</mml:mi><mml:mo>=</mml:mo><mml:mi>Cr</mml:mi><mml:mo>,</mml:mo><mml:mspace width="0.16em"/><mml:mi mathvariant="normal">V</mml:mi><mml:mo>;</mml:mo><mml:mspace width="0.16em"/><mml:mi>X</mml:mi><mml:mo>=</mml:mo><mml:mi mathvariant="normal">S</mml:mi><mml:mo>,</mml:mo><mml:mspace width="0.16em"/><mml:mi>Se</mml:mi></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> by controlling the interlayer interaction and dimension
Xunkai Duan, Hua Wang, Xiaofang Chen, Jingshan Qi
Abstract
Magnetoelectric multiferroic materials are the potential candidates for the high-density nonvolatile data storage devices. However, up to now, multiferroic materials with strong magnetoelectric coupling are still rare. Here, based on the first-principles calculations and theoretical model, we predict a different class of single phase multiferroic materials, transition metal phosphorus chalcogenides $TM{\mathrm{P}}_{2}{X}_{6}(T=\mathrm{Cu},\phantom{\rule{0.16em}{0ex}}\mathrm{Ag};\phantom{\rule{0.16em}{0ex}}M=\mathrm{Cr},\phantom{\rule{0.16em}{0ex}}\mathrm{V};\phantom{\rule{0.16em}{0ex}}X=\mathrm{S},\phantom{\rule{0.16em}{0ex}}\mathrm{Se})$ with multiple polarization phases and strong magnetoelectric coupling. The ferroelectric polarization originates from the movement of Cu/Ag atoms breaking the symmetry of spatial inversion and the magnetism arises from partially filled $d$ orbitals of the V/Cr atoms. It is predicted that the different ferroelectric phases of $TM{\mathrm{P}}_{2}{X}_{6}$ bulk have different band gaps, providing a way to control electronic and transport properties by the external electric field. Most prominently, for $\mathrm{CuV}{\mathrm{P}}_{2}{\mathrm{S}}_{6}$ bilayer and few layers, one of the ferroelectric phases has ferromagnetic ground state and the other has antiferromagnetic states, realizing the electric-field control of magnetism. We reveal that the physical mechanism of the strong magnetoelectric coupling is from the reduced dimension and symmetry by constructing a theoretical model including the crystal field splitting, electric polarization effect, and exchange interaction. This work not only predicts a different class of magnetoelectric multiferroic materials, but also proposes a strategy to design them by controlling the interlayer interaction in van der Waals layered materials.