Local-moment ferromagnetism and unusual magnetic domains in Fe_(1/4)TaS₂ crystals

Single crystals of Fe$_{1/4}$TaS$_{2}$ have been studied by using magneto-optical (MO) imaging and radio-frequency (rf) magnetic susceptibility, $\chi$. Real time MO images reveal unusual, slow dynamics of dendritic domain formation, the details of which are strongly dependent upon magnetic and thermal history. Measurements of $\chi(T)$ show well-defined, local moment ferromagnetic transition at $T\approx 155$ K as well as thermal hysteresis for 50 K$<T<$60 K. This temperature range corresponds to the domain formation temperature as determined by MO. Together these observations provide strong evidence for local moment ferromagnetism in Fe$_{1/4}$TaS$_{2}$ crystals with large, temperature dependent magnetic anisotropy.