We report here the effect of annealing temperature T_ann (200–600 °C) on the structural, mechanical, and magnetic properties of Cd_0.40M_0.60ZnO₂ (M = Mn, Ni) nanocomposites. The increase in T_ann correlates with a significant change in unit cell volume (V), porosity (PS) crystallite size (D_hkl), particle size (r), Debye temperature (θ_D) and elastic modulus(Y). The values of V, r, θ_D and Y are higher for the Mn-series than Ni. While the values of PS and D_hkl are higher for Mn than Ni at T_ann ≤ 300 °C, and the reverse is true at T_ann ≥ 400 °C. The average particle size is 10.6 ± 2.4 nm for Mn-series, but it is decreased to 7.5 ± 4.0 nm for Ni-series, indicating quantum-dot size. Surprisingly, both series exhibit ferromagnetic behavior as T_ann increases to 600 °C, but the magnetization parameters for the Mn series are higher than those for Ni. Furthermore, the anisotropy field (H_a) is about 350 times higher than the corrective field (H_c), indicating hard magnetic materials. The switching field distribution (SFD) is increased by annealing, but it is higher for Ni-series than Mn. The considered nanocomposites would be useful for altering plastic deformation and spintronic devices.