Magnetic Resistivity in Bi2Sr2Ca(Cu1-xCox)2Od Epitaxial Thin Films

The scaling behavior of the effective activation energy of high-quality epitaxial c-oriented Bi₂Sr₂Ca(Cu_1-xCo_x)₂O_d thin films with 0≤x ≤0.025 has been studied as a function of temperature and magnetic field. For all samples, the effective activation energy scales as U(T, μ_oH)=Uo(1-T/T_c)^mHⁿ with exponent m=1.25±0.03, n=-1/2 and the field scaling 1/μ_oH and -Uμ_oH for thick films and ultra thin films, respectively. The results are discussed taking into account of the influence of the Co substitution with a model in which U(T, H) arises from plastic deformations of the viscous flux liquid above the vortex-glass transition temperature.