  The cryptoferromagnetic state (the state with intrinsic domain structure) in
superconducting ferromagnets subjected to external magnetic field is studied
theoretically. Ferromagnetism originates either from electron spin or the
intrinsic angular momentum of Cooper pairs (chiral p-wave superconductors like
$\mathrm{Sr_2 Ru O_4}$). The phase transitions towards the Meissner and the
mixed states are investigated, and the magnetic phase diagrams are obtained.
Cryptoferromagnetism, as a form coexistence of superconductivity and
ferromagnetism, can be detected by observation of magnetization curves
predicted in the present analysis.
