  We report on a monotonic reduction of Curie temperature in dilute
ferromagnetic semiconductor (Ga,Mn)As upon a well controlled
chemical-etching/oxidizing thinning from 15 nm down to complete removal of the
ferro- magnetic response. The effect already starts at the very beginning of
the thinning process and is accompanied by the spin reorientation transition of
the in-plane uniaxial anisotropy. We postulate that a negative gradient along
the growth direction of self-compensating defects (Mn interstitial) and the
presence of surface donor traps gives quantitative account on these effects
within the p-d mean field Zener model with adequate mod- ifications to take a
nonuniform distribution of holes and Mn cations into account. The described
here effects are of practical importance for employing thin and ultrathin
layers of (Ga,Mn)As or relative compounds in concept spintronics devices, like
resonant tunneling devices in particular.
