Kavli Affiliate: David T. Limmer
| First 5 Authors: Isaac M. Craig, B. Junsuh Kim, David T. Limmer, D. Kwabena Bediako, Sinéad M. Griffin
| Summary:
Van der Waals hosts intercalated with transition metal (TM) ions exhibit a
range of magnetic properties strongly influenced by the structural order of the
intercalants. However, predictive computational models for the intercalant
ordering phase diagram are lacking, complicating experimental pursuits to
target key structural phases. Here we use Density Functional Theory (DFT) to
construct a pairwise lattice model and Monte Carlo to determine its associated
thermodynamic phase diagram. To circumvent the complexities of modeling
magnetic effects, we use the diamagnetic ions Zn$^{2+}$ and Sc$^{3+}$ as
computationally accessible proxies for divalent and trivalent species of
interest (Fe$^{2+}$ and Cr$^{3+}$), which provide insights into the
high-temperature thermodynamic phase diagram well above the paramagnetic
transition temperature. We find that electrostatic coupling between
intercalants is almost entirely screened, so the pairwise lattice model
represents a coarse-grained charge density reorganization about the
intercalated sites. The resulting phase diagram reveals that the
entropically-favored $sqrt{3} times sqrt{3}$ ordering and coexisting locally
ordered $sqrt{3} times sqrt{3}$ and $2 times 2$ domains persist across a
range of temperatures and intercalation densities. This occurs even at quarter
filling of interstitial sites (corresponding to bulk stoichiometries of
M$_{0.25}$TaS$_2$; M = intercalant ion) where a preference for long-range $2
times 2$ order is typically assumed.
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