Theoretical investigation on pyrochlore melanothallite Cu2OCl2

Tsung-Wen Yen^1,2*, 黃信銘¹

¹物理系, 國立中山大學, 高雄市, Taiwan
²晶體研究中心, 國立中山大學, 高雄市, Taiwan

* Presenter:Tsung-Wen Yen, email:peteryen2017@gmail.com

Recently, Cu2OCl2 attracts much attention due to its pyrochlore lattice which is a tetrahedral corner-sharing structure. The Cu atom on each of its tetrahedral corners carries an S =1/2 spin, forming a spin frustrated system. Experimentally, the nonmagnetic Fddd structure becomes unstable at around 70 K and undergoes an (anti)ferroelectric as well as a magnetic phase transition. From neutron powder diffraction measurements, the magnetic structure is noncollinear and incommensurate with a propagation vector of (0.827 0 0). In this work, we evaluate some possible lattice and spin structures by performing incommensurate spin spiral calculations in the ab initio software VASP and discover a spin-triggered lattice distortion into an Fdd2(a) lattice, which breaks inversion symmetry so as to induce ferroelectricity correspondingly.

Keywords: multiferroic materials, pyrochlore , ab initio methods, spin spirals, spin frustrated system