Logarithmic enhancement of low temperature electrical resistivity at high magnetic fields in NbTi alloys

The low temperature electrical resistivity ρ{variant}(T) of five NbTi alloys, Nb₃Ti₇₉, Nb₃Ti₆₆, Nb₄₈Ti₅₂, Nb₆₃ Ti₃₇ and Nb₉₁Ti₉, in magnetic fields up to 20.6 T has been investigated. At 20.6 T a slight but definite enhancement of ρ{variant}(T) with logarithmic temperature dependence is observed in all the samples except Nb₉₁Ti₉ below a temperature T_m where ρ{variant}(T) takes a minimum. The enhancement appears remarkably in Ti-rich alloys. These samples exhibit positive magnetoresistance which tends to saturate as the field increases. In Nb₂₁Ti₇₉ and Nb₆₃Ti₃₇ with lower H_c2 the resistivity at 1.5 K reaches a saturated value above 15 T and 17 T, respectively. These fields correspond to about 1.5 times the value of H_c2 (1.5 K). An anomalous contribution in ρ{variant}(T) cannot be seen for Nb₉₁Ti₉, poor in Ti. Characteristics of the enhancement of ρ{variant}(T) are reported in detail and discussed in relationship with Ti-concentrations and metasble phases in the β-matrix.