 A Powerful Local Shear Instability in Weakly Magnetized Disks. I. Linear Analysis by Steven A. Balbus and John F. Hawley

The Astrophysical Journal 376, pp.214–222. Sections2.1–2.3 give the local linear dispersion and stability criterion; section2.5 explains the magnetic-tension mechanism. The hosted PDF also includes the companion nonlinear-evolution paper after the first article.