Condensed-Matter Physics & Materials Science Seminar

Abstract: I will present our recent neutron scattering studies of magnetic excitations in the ilmenite CoTiO3, with a Co2+ magnetic sublattice formed by ABC stacked honeycomb layers. This material acquires an easy-plane A-type antiferromagnetic order below TN=38K. Despite its simple crystal and magnetic structure, this material has been recognized as an excellent model system for many interesting phenomena such as bond-dependent anisotropic spin interactions [1], quantum order by disorder [2], topological magnons [3] and collective spin orbital excitations [4]. In the first part of the talk, I will discuss the low energy magnon excitations in CoTiO3, and its modelling using linear spin wave theory. Our results provide direct evidence for a dominant XY-like magnetic interaction in CoTiO3, which gives rise to a Dirac-cone like magnon dispersion observed in this material. I will also present our most recent high-resolution neutron scattering results in the presence of an in-plane magnetic field and discuss their implications on the nature of exchange anisotropy in this material. In the second part of the talk, I will present our temperature dependence study of the spin orbiton dynamics in CoTiO3, which we explained using a simple multilevel model. We found compelling evidence for mixing between the ground and excited spin orbital states in this material that are normally neglected in transition metal systems. I will conclude by discussing the importance of our results in the context of spin orbital physics in heavy transition metal materials.
[1] Huimei Liu et al., Phys. Rev. Lett., 125, 047201 (2020)
[2] M Elliot et al., Arxiv: 2007.04199 (2020)
[3] Bo Yuan et al., Phys. Rev. X, 10, 011062 (2020)
[4] Bo Yuan et al., Phys. Rev. B, 102, 134404 (2020)