Evidence for Multicritical Behavior in Nanostructured Mn-intercalated TaS$_2$

Nanostructured Mn-intercalated TaS$_2$ was prepared with a nominal Mn concentration of 25{\%}. The sample consisted of nanotube structures with diameters between 30 nm and 300 nm. X-ray diffraction measurements indicated that the Mn was incorporated into intercalation sites between the TaS$_2$ layers. The sample exhibited Curie-Weiss behavior virtually all the way down to the Curie-Weiss temperature of 91 K, demonstrating the absence of significant chemical clustering and short-range order in the paramagnetic regime. Magnetization versus temperature measurements indicated a ferromagnetic transition at $\sim$90 K, which is somewhat higher than that for bulk crystalline Mn$_{0.25}$TaS$_2$. An Arrott plot confirms the ferromagnetic transition at 87 K, with critical exponents close to mean-field values. However, ac susceptibility measurements in the presence of a dc bias field suggest the presence of another transition at 81 K, with critical exponents much larger than mean-field values. A scaling plot using these unusual exponents exhibited excellent collapse of the data. We interpret this behavior in terms of a nearby multicritical point, with the system exhibiting re-entrant cluster-glass behavior.