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We study the loop-induced flavor-changing decay t→ c+ γ in a nonlinear R ξ gauge for the standard model with three and four generations and in models with two Higgs doublets. We find that this decay could be relevant only in a scenario with two Higgs doublets and the mass of the fourth-generation b′ quark larger than m t. Under these conditions, the flavor-changing electromagnetic decays T q*→ D q γ (T q→ D q* γ) may surpass the standard electromagnetic transition T q*→ T q γ.