In 122-ferropnictides, superconductivity can be induced either by iso- or aliovalent chemical substitution or by applying a mechanical pressure to the antiferromagnetic parent compounds. In particular, one can introduce extra electrons or holes into the FeAs layers by replacing Fe with Co [Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ or Ba with K [Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$], respectively. In the case of Mn substitution, one might naively expect a hole-doped system similar to Ba$_{1-x}$K$_{x}$Fe$_2$As$_2$, but in reality a completely different phase diagram is observed \cite{Kim10}. It exhibits no superconductivity, but contains a novel antiferromagnetic phase that does not break the tetragonal symmetry of the crystal, in contrast to the spin-density-wave (SDW) state in the parent compound. Additionally, the magnetic transition temperatures above 10\%-Mn doped BaFe$_2$As$_2$ start to increase, evidencing that this magnetic state is strongly related to the presence of Mn. However, its m!
icroscopic origin still remains unexplained up to now. Thus, we carried out complementary experimental methods $\mu$SR and neutron spectroscopy on 12\%-Mn doped BaFe$_2$As$_2$ to investigate the magnetic property of such novel phase, and observed the distinct behavior of magnetism in sharp contrast to the SDW in the BaFe$_2$As$_2$ compound. In this (talk/poster), we will discuss about possible origins of novel magnetic phase in 12\%-Mn doped BaFe$_2$As$_2$.
\bibitem{Kim10} M.\,G.\, Kim \textit{et al.}, Phys. Rev. B \textbf{82}, 220503(R) (2010).
