Magnetic structure of rhombohedral honeycomb antiferromagnets

We propose to determine details of the magnetic structure in the layered honeycomb easy-plane magnet CoTiO3, with ferromagnetic honeycomb layers stacked antiferromagnetically. In recent inelastic measurements on MERLIN we observed a spin gap at low energies, suggesting a preferential orientation of the moments. This is unexpected as no local anisotropy is allowed for Kramers ions and the three-fold symmetry of the crystal structure ensures that no anisotropic bilinear spin exchanges can select a unique moment orientation in the ab plane. The ground state selection could be due to quantum zero-point fluctuations, here we plan to search for evidence of a substantial reduction of the ordered moment expected if this mechanism was applicable. We also propose complementary and contrasting measurements on the easy-axis FeTiO3, where an almost full ordered moment is expected along the c-axis.

我们提出对层状蜂窝易面磁体钛酸钴(CoTiO3)的磁结构细节开展研究，该材料的铁磁性蜂窝层以反铁磁性方式堆叠。此前我们在MERLIN谱仪上开展的非弹性散射测量中，观测到低能区域存在自旋隙，这表明磁矩存在优先取向。这一现象出乎意料：克拉默斯离子(Kramers ions)不存在局域各向异性，且晶体结构的三重对称性确保了ab平面内不存在能够唯一选定磁矩取向的各向异性双线性自旋交换相互作用。基态的取向选择可能源于量子零点涨落，本次研究中我们计划搜寻相关证据，以验证若该机制成立，预期的有序磁矩会出现显著衰减这一猜想。我们还提议对易轴型钛酸铁(FeTiO3)开展互补性与对照性测量，该材料沿c轴方向预期存在近乎完整的有序磁矩。