  We present a multichannel quantum-defect theory for magnetic Feshbach
resonances in the interaction of two heteronuclear group I atoms. The theory
provides a unified and a uniform description of resonances in all partial
waves, and enables the characterization of large number of resonances in terms
of very few parameters. For the sample system of $^6$Li$^{40}$K, we present
descriptions of all resonances in $aa$, $ab$, and $ba$ channels, in partial
waves $s$ ($l=0$) through $h$ ($l=5$), and in a magnetic field of 0 through
1000 Gauss. All resonances, including those in nonzero partial waves, are fully
characterized using the newly developed parametrization of Gao [Phy. Rev. A
\textbf{84}, 022706 (2011)].
