  The magnetic and electronic properties of the magnetically doped topological
insulator Bi$_{\rm 2-x}$Mn$_{\rm x}$Te$_3$ were studied using electron spin
resonance (ESR) and measurements of static magnetization and electrical
transport. The investigated high quality single crystals of Bi$_{\rm
2-x}$Mn$_{\rm x}$Te$_3$ show a ferromagnetic phase transition for $x\geq 0.04$
at $T_{C}\approx 12$ K. The Hall measurements reveal a p-type finite
charge-carrier density. Measurements of the temperature dependence of the ESR
signal of Mn dopants for different orientations of the external magnetic field
give evidence that the localized Mn moments interact with the mobile charge
carriers leading to a Ruderman-Kittel-Kasuya-Yosida-type ferromagnetic coupling
between the Mn spins of order 2-3 meV. Furthermore, ESR reveals a
low-dimensional character of magnetic correlations that persist far above the
ferromagnetic ordering temperature.
