  In antiferromagnets, the interplay of spin frustration and spin-lattice
coupling has been extensively studied as the source of complex spin patterns
and exotic magnetism. Here, we demonstrate that, although neglected in the
past, the spin-lattice coupling is essential to ferrimagnetic spinels as well.
We performed ultrahigh-field magnetization measurements up to 110 T on a
Yafet-Kittel ferrimagnetic spinel, MnCr$_2$S$_4$, which was complemented by
measurements of magnetostriction and sound velocities up to 60 T. Classical
Monte Carlo calculations were performed to identify the complex high-field spin
structures. Our minimal model incorporating spin-lattice coupling accounts for
the experimental results and corroborates the complete phase diagram, including
two new high-field phase transitions at 75 and 85 T. Magnetoelastic coupling
induces striking effects: An extremely robust magnetization plateau is embedded
between two unconventional spin-asymmetric phases. Ferrimagnetic spinels
provide a new platform to study asymmetric and multiferroic phases stabilized
by spin-lattice coupling.
