  It is argued that the stress caused by vortex cores in the mixed state of
superconductors may result in a field dependent contribution to the free energy
and magnetization of measurable levels. For sufficiently strong stress
dependence of the critical temperature, $\partial T_c/\partial p$, this
contribution may result in the so-called "second peak" in the field dependence
of the reversible magnetization, the effect often masked by vortex pinning and
creep.
