  We present a study of the magnetocaloric effect in metallic systems
exhibiting first-order magnetic transitions and focus on consequences of
magnetic phase separation. We account for ferrimagnetic, ferromagnetic, and
Neel antiferromagnetic order. Based on the archetypal Hubbard model being
treated within the mean-field approximation, we provide and explore its
implications on the field-induced entropy change in metallic system with phase
separation. Chosen framework allows us to properly analyze phase volumes'
dependence on parameters of phase-separated (PS) system. Moreover, an account
for phase separation boundaries as functions of magnetic field provides a
natural splitting of the PS region, where each subregion corresponds to a
different temperature dependence of entropy change: moving from one subregion
to the other produces a kink, followed by a strong linear growth of entropy
change. We encounter a second-order magnetic transition from paramagnetic to
antiferromagnetic phase in PS region that occurs for particular parameter
values. Despite the fact that both phases have zero total magnetization, the
transition has a strong impact on entropy change.
