Magnetism of SmFeAsO1-xFx

Magnetic properties of superconducting SmFeAsO$_{1-x}$F$_{x}$ are demonstrated by $^{57}$Fe Mossbauer spectroscopy (MS) and $^ {149}$Sm Nuclear resonant forward scattering (NRFS). Polycrystalline SmFeAsO$_{1- x}$F$_{x}$ samples were synthesized using two-step solid state reaction described elsewhere. [New J. Phys. 12, 033005 (2010).] Purity of samples was checked by X-ray diffraction patterns using Cu K-alpha radiation. Resistivity and magnetization measurements, as well as by $^{57}$Fe MS and $^ {149}$Sm NRFS spectroscopy, at various temperatures were performed to define superconducting, magnetic ordering temperatures. [Phys. Rev. B 78, 184512 (2008) {\&} J. Phys. Soc. Japan 77, 103706 (2008).] A magnetic phase diagram we have proposed is closer to that by Hess et al [Europhys. Lett. 87, 17005 (2009).]; that is long-range AF ordering of Fe (a static magnetism) does not persist in the superconducting regime. Such a relation between spin dynamics and SC is a common feature among LnFeAsO$_{1-x}$F$_{x}$ (Ln = La, Ce, Pr, Nd, and Sm). Our results indicate that the relation between the static magnetism and $T_{c}$ of LnFeAsO$_{1-x}$F$_{x}$ shows similar topology to that of copper-based high-Tc superconductors. [Phys. Rev. B 42, 7981 (1990).]