Comparison of magnetic behavior in nanostructured and crystalline forms of an intercalated dichalcogenide

We have made temperature- and field-dependent dc magnetization and ac susceptibility measurements on polycrystalline Mn-intercalated TaS₂ (Mn_xTaS₂) for concentrations x of Mn in the range 0.15 ≤ x ≤ 0.25. This magnetic behavior was compared with previously reported results for nanostructured Mn_xTaS₂ with 0.15 ≤ x ≤ 0.24. The crystalline samples exhibited a paramagnetic to ferromagnetic (PM to FM) transition even for the lowest Mn concentration investigated (x = 0.15). The Curie temperature exhibited a peak as x decreased. This non-monotonic behavior is consistent with the RKKY interaction. The nanostructured material exhibited cluster-glass behavior at the lowest concentrations (x ~ 0.15) and a PM to FM transition at higher x values. For x = 0.24, nanostructured Mn_xTaS₂ is a re-entrant cluster glass. Scaling of the ac susceptibility for the crystalline samples yielded a gap exponent Δ = γ + β slightly greater than 2 whereas corresponding values for nano-Mn_xTaS₂ were anomalously high (> 4). The differences in behavior are attributed to clustering effects attendant to the spatial distribution of Mn ions in the two morphologies.