Magnetoresistivity and $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ in ${\mathrm{MgB}}_2$

Detailed magnetotransport data on dense wires of ${\mathrm{MgB}}_2$ are reported for applied magnetic fields up to 18 T. The temperature and field dependencies of the electrical resistivity are consistent with ${\mathrm{MgB}}_2$ behaving like a simple metal and following a generalized form of Kohler’s rule. In addition, given the generally higher-$T_c$ values and narrower resistive transition widths associated with ${\mathrm{MgB}}_2$ synthesized in this manner, combined with applied magnetic fields of up to 18 T, an accurate and complete $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ curve could be determined. This curve agrees well with curves determined from lower field measurements on sintered pellets and wires of ${\mathrm{MgB}}_2.$ $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ is linear in T over a wide range of temperature $(7\mathrm{}\mathrm{K}<~T<~32\mathrm{K})$ and has an upward curvature for T close to $T_c.$ These features are similar to other high κ, clean limit, boron-bearing intermetallics: ${\mathrm{YNi}}_2{\mathrm{B}}_2\mathrm{C}$ and ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}.$