[en] The hysteretic behavior of mechanically alloyed nanocomposites FeCo+MnO was studied at high temperatures. These composites present an unusual high and thermally stable coercivity, compared to FeCo milled at equal conditions. Coercivity enhancement was observed in hysteresis loops obtained between room temperature and 750 K. It is attributed to the isolation of the FeCo ferromagnetic particles by the paramagnetic MnO (T_N=120 K). The M_rev(M_irr)_H curves are clearly linear for the composite, indicating that coherent rotation is the reversal mechanism in these materials