  We perform a microscopic study of itinerant ferromagnetic systems. We reveal
a very rich phase diagram in the three-dimensional space spanned by the
chemical potential, a magnetic field, and temperature beyond the Landau theory
analyzed so far. Besides a generic wing structure near a tricritical point upon
introducing the magnetic field, we find that an additional wing can be
generated close to a quantum critical end point (QCEP) and also even from
deeply inside the ferromagnetic phase. A tilting of the wing controls the
entropy jump associated with the metamagnetic transition. Ferromagnetic and
metamagnetic transitions are usually accompanied by a Lifshitz transition at
low temperatures, i.e., a change of Fermi surface topology including the
disappearance of the Fermi surface. In particular, the Fermi surface of either
spin band vanishes at the QCEP. These rich phase diagrams are understood in
terms of the density of states and the breaking of particle-hole symmetry in
the presence of a next nearest-neighbor-hopping integral t', which is expected
in actual materials. The obtained phase diagrams are discussed in a possible
connection to itinerant ferromagnetic systems such as UGe2, UCoAl, ZrZn2, and
others including materials exhibiting the magnetocaloric effect.
