Speaker
Description
NiI$_2$ is a layered van der Waals magnet which has recently been proposed to host a novel form of skyrmion phase in the 2D limit$^1$. $\mu$SR has proven to be a sensitive probe of magnetic dynamics resulting from such topological excitations. I will present the results$^2$ of $\mu$SR measurements of NiI$_2$, which probe magnetic phase transitions at $T_{\rm{N1}}=73$ K and $T_{\rm{N2}}=62$ K. Supporting density functional theory calculations will be discussed which allow the determination of a muon stopping site whose magnetic environment is consistent with the proposed ground-state magnetic structure. Measurements of dynamics reveal behavior consistent with spin-wave excitations below $T_{\rm{N2}}$. In the region $T_{\rm{N2}}$<$T$<$T_{\rm{N1}}$ the character of the dynamics changes qualitatively, resulting in an unusual region of temperature-independent fluctuations. Our measurements, combined with a group theoretical analysis of the Ni electron orbitals, show that the changes in magnetic behavior between these two temperature regions are possibly caused by a subtle shift in the material's structural symmetry at $T_{\rm{N2}}.$ This work demonstrates how a combination of techniques in support of $\mu$SR measurements can lead to greater insight into the results of experiments and our conclusions shed new light on the driving forces behind the rich magnetism hosted by this material.
$^1$D. Amoroso et al. Nat. Comm. 11, 5784 (2020)
$^2$T. L. Breeze et al. PRB 111, 104420 (2025)
| theodore.l.breeze@durham.ac.uk | |
| Funding Agency | EPSRC |
| Supervisors Name | Tom Lancaster |
| Supervisors Email | tom.lancaster@durham.ac.uk |
| Did you request an Invitation Letter for a Visitors Visa Application | No |
