On the magnetic tricritical point in BaFe$_{2(1-x)}$Co$_{2x}$As$_{2}$*

We present here high resolution magnetization measurements on high-quality BaFe$_{2(1-x)}$Co$_{2x}$As$_{2}$, 0$\leq$x$\leq$0.046 as-grown single crystals. The results confirm the existence of a magnetic tricritical point in the ($x$,$T$) plane at x$^{m}_{tr}$$\approx$0.022 [1,2]. We show that the extrapolated T$_{c}$ onset doping could be close to the magnetic tricritical point x$^{m}_{tr}$. It has been speculated that the magnetic critical point is relevant to the superconductivity in this series [3]. Finally, we comment on the universality of the tricritical point in the superconducting 122s.\\[4pt] [1] M. G. Kim \emph{et al.}, Phys. Rev. B {\bf 83}, 134522 (2011).\\[0pt] [2] C. R. Rotundu and R. J. Birgeneau, Phys. Rev. B {\bf 84}, 092501 (2011).\\[0pt] [3] G. Giovannetti \emph{et al.}, Nature Communications {\bf 2}, article number 398 (2011).