Muons and magnets

Abstract:

We report muon-spin relaxation (μ+SR) measurements of copper acetate [Cu(CH3CO2)2·H2O], a model spin-1/2 Heisenberg antiferromagnetic dimer chain with an alternation parameter α = 0.001. Zero-field μ+SR data collected from 2 to 200 K revealed an oscillatory asymmetry that was analyzed using a model based on the muon-stopping site determined by density-functional theory +μ calculations. Below 50 K, the fitted parameters capture spin dynamics characteristic of the singlet ground state, while at higher temperatures, an additional relaxation was observed due to the thermally populated triplet state, affecting the local magnetic field around the muon-stopping site. The temperature dependence of the fitting parameters was found to exhibit characteristics similar to those of a bipartite entanglement measure, “distance between the states,” obtained from the magnetic susceptibility data. Longitudinal-field μ+SR measurements reveal field-dependent relaxation at field values much lower than the field values required to close the spin singlet-triplet gap, emphasizing the importance of quantum fluctuations in the spin dynamics of the dimerized copper acetate.

Abstract:

We present the results of muon-spin relaxation $\left(\mu \mathrm{SR}\right)$ measurements of the static and dynamic magnetism of $M_{1/3}{\mathrm{NbS}}_2$ $(M=\mathrm{Fe}, \mathrm{V}, \mathrm{Mn})$ , three intercalated transition-metal dichalcogenides. Transitions to long-range magnetic order are observed in all three materials, and local magnetic fields at muon sites are compared to dipole field calculations. Measurements on ${\mathrm{Fe}}_{1/3}{\mathrm{NbS}}_2$ capture the evolution of two coexisting magnetic phases. In ${\mathrm{V}}_{1/3}{\mathrm{NbS}}_2$ , we observe a peak in the dynamic response at 9 K, coincident with previous reports of a possible low-temperature phase transition. The observation of high-frequency muon precession in ${\mathrm{Mn}}_{1/3}{\mathrm{NbS}}_2$ suggests the existence of an additional muon site that implies a difference in the electronic energy landscape compared to the other materials in the series. Taken together, this demonstrates that the change in intercalant species drives significant variations in magnetism, highlighting the $M_{1/3}{\mathrm{NbS}}_2$ series as an ideal group of materials for investigating a wide range of magnetic phenomena.