  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}$$\approx$0.022 and reveal the emergence of the
heat capacity anomaly associated with the onset of the structural transition at
x$^{s}$$\approx$0.0064. We show that the samples with doping near x$^{m}_{tr}$
do not show superconductivity, but rather superconductivity emerges at a
slightly higher cobalt doping, x$\approx$0.0315
