  Measurements of the Hall effect, thermoelectric power, magnetic
susceptibility and upper and lower critical fields were performed on single
crystals of SrFe(2-x)Ni(x)As2, an FeAs-based superconducting system that
exhibits a reduced superconducting transition temperature Tc in comparison to
most other iron-pnictide superconductors. Studies of the Hall and
thermoelectric responses indicate that Ni substitution in this system results
in a dominant electron-like response, consistent with electron doping in other
similar systems but with a weaker change in the Hall coefficient and a more
gradual change in the thermoelectric response with Ni concentration. For
optimally doped samples with full superconducting volume fraction, the lower
and upper critical fields were determined to be Hc1(1.8 K)= 0.08T and Hc2(0)=
25T, respectively, with lower-Tc samples showing reduced values and indications
of inhomogeneous superconductivity. Comparable to other higher-Tc FeAs-based
materials, the temperature dependence of the upper critical field, dHc2/dT, is
linear over a wide temperature range, and the large values of Hc2(0) greatly
exceed conventional estimates of paramagnetic and orbital limits.
