  The appearance of magnetization during the application of mechanical stress
and the creation of elastic deformation during the application of a magnetic
field are two fundamental properties of piezomagnetic materials. The symmetry
of superconducting ferromagnets UGe_2, URhGe, UCoGe allows piezomagnetism. In
addition to conventional piezomagnetic properties occurring in both normal and
superconducting states, superconducting state of these piezomagnets has its own
specificity. Unlike conventional superconductors, in uranium ferromagnets, the
critical transition temperature to the superconducting state changes its value
when the direction of the field changes to the opposite.
