Magnetic Pair-Breaking in Y_1-xHo_xNi₂B₂C ( x=0, 0.25, 0.5, 0.75) Single Crystals

Temperature-dependent resistivity and magnetic susceptibility were studied for quaternary borocarbide intermetallic compounds Y_1-xHo_xNi₂B₂C (x=0, 0.25, 0.5, 0.75), which show coexistence of superconductivity with magnetism. In a normal state, the compounds exhibit conventional metallic behaviour. The Debye temperature θ_D is derived by fitting the temperature dependence of resistivity to the Bloch--Gruneisen expression, i.e. θ_D scales with M^-0.5 (M is the averaged atomic mass on the Y³⁺ site), which means that the acoustic mode of the lattice vibrating spectrum is influenced by the Y³⁺ site atoms. Fitting the temperature-dependent magnetic susceptibility above T_N to the Curie--Weiss law, effective magnetic moment μ_eff is deduced, and then de Gennes factor dG is calculated. It is found that as Ho content increases, μ_eff as well as dG increases and T_C decreases. Moreover, the decrease of T_C scales with dG, i.e., Δ T_C ∝ -nI² N(ε_F)dG, which is consistent with the prediction of the Abrikosov--Gor'kov theory. We suggest that the depression of T_C could be mainly ascribed to the magnetic pair-breaking effect of magnetic Ho³⁺ ions. The change of Debye temperature with Ho content may not have significant impact on T_C.