  Metamagnetism in layered ruthenates has been interpreted as a novel kind of
quantum critical behavior. In an external magnetic field,
Ca$_{2-x}$Sr$_x$RuO$_4$ undergoes a metamagnetic transition accompanied by a
pronounced magnetostriction effect. In this paper we present a mean-field study
for a microscopic model that naturally reproduces the key features of this
system. The phase diagram calculated is equivalent to the experimental $T$-$x$
phase diagram. The presented model also gives a good basis to discuss the
critical metamagnetic behavior measured in the system.

Strongly Correlated Electrons