Epitaxial thin films of double perovskite Y(Ni_0.5Mn_0.5)O₃(001) and Y(Ni_0.5Mn_0.5)O₃(101) grown on SrTiO₃(001) and SrTiO₃(111), respectively, were studied by XPS and SQUID magnetometer. Temperature dependent Ti diffusion was detected in the Y(Ni_0.5Mn_0.5)O₃(101)/SrTiO₃(111) samples, while no diffusion was observed in Y(Ni_0.5Mn_0.5)O₃(001)/SrTiO₃(001) samples. It was observed that the use of a low ablation rate promoted ionic migrations, mainly due to the associated annealing time that samples undergo when grown at lower rates. The migration speed was determined by XPS analysis and its influence on the magnetic properties of the Y(Ni_0.5Mn_0.5)O₃ (101) films was characterized and discussed