  We consider a semiconducting carbon nanotube (CNT) laying on a ferromagnetic
insulating sub-strate with one end depassing the substrate and suspended over a
metallic gate. We assume that the polarised substrate induces an exchange
interaction acting as a local magnetic field for the electrons in the
non-suspended CNT side. Generalizing the approach of I. Snyman and Yu.V.
Nazarov [Phys. Rev. Lett. 108, 076805 (2012)] we show that one can generate
electrostatically a tun-able spin-polarized polaronic state localized at the
bending end of the CNT. We argue that at low temperatures manipulation and
detection of the localised quantum spin state is possible.
