Giant magnetic coercivity and nano-domains in Fe$_{0.25}$TaS$_2$*

We have explored giant magnetic coercivity (H$_c \sim$ 7 tesla) in the highly anisotropic ferromagnet of Fe$_{0.25}$TaS$_2$ through harnessing order of Fe$^{2+}$ ions intercalated in-between TaS$_2$ layers. Fe ions order well in annealed crystals and form a (1/2,0,0) superlattice. However, a (1/3,1/3,0) superlattice, in addition to the (1/2,0,0) superlattice, can form in quenched crystals. These coexisting superlattices with nano-size domains result in significant change of zero-field-cooled magnetic domain configurations and huge enhancement of H$_c$, probably through efficient magnetic domain wall pinning by nano-size superlattice domains.\footnote{Y.J. Choi, et al, EuroPhys. Lett., 86, 37012 (2009).}