Theoretical investigation on pyrochlore melanothallite Cu2OCl2

Tsung-wen Yen^2*, Shin-ming Huang²

¹Center for Crystal Researches, National Sun yat-sen University, Kaohsiung, Taiwan
²Physics department, National Sun yat-sen university, Kaohsiung, Taiwan

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

Recently, the discovery of multiferroicity in the pyrochlore-like compound Cu2OCl2 has generated significant interest, and several studies have been performed in this area. This transition metal oxychloride is unique because the divalent copper atoms create an S = 1/2 correlated insulator and the pyrochlore lattice tends to frustrate spins. From neutron powder diffraction measurements, an incommensurate magnetic order of the ordering vector q = (0.827,0,0) emerges below the Néel temperature of 70 K. At this temperature or slightly above, ferroelectricity (FE) or antiferroelectricity, accompanying a lattice distortion, has been observed. Experimentally, some discrepancies remain. In this paper, we report our first-principles simulation results by evaluating the possible lattice and spin spiral states. We found that the Fddd structure is not more stable than Fdd2(a), which is supported by our reexamination of the x-ray diffraction data. In addition, we find that after we include magnetism in the calculation, it predicts that the Fdd2(a) lattice with a helical (proper screw) spin structure is energetically more stable than other spin configurations. Our results indicate charge-order-driven FE that subsequently induces magnetism.

Keywords: Pyrochlore, Multiferroic, spin spirals, ab initio calculation, VASP