Observation of an antiparallel magnetic state in Fe3O4/Mn3O4 superlattices

[Fe3O4(20 A)/Mn3O4(80 A)]x20 and [Fe3O4(20 A)/MgO(80 A)]x20 superlattices on MgO(001) are fabricated by molecular beam epitaxy in order to compare the magnetic coupling in ferrimagnetic–ferrimagnetic and ferrimagnetic–nonmagnetic systems. The magnetic response is measured as a function of applied-field (−50 to 50 kOe) parallel to the film surface and temperature (5–300 K). A strong reduction of magnetization, from 115 to 45 emu/cm3, is observed only from the Fe3O4/Mn3O4 superlattice at temperature below ∼60 K. This observation indicates that the magnetic moments in two constituents are antiparallel and the Curie temperature (Tc) of Mn3O4 is enhanced for 15 K. In addition, the remanent magnetization shows a compensation point (Tcp) at about 32 K at which the opposing spins are balanced. Detailed magnetic hysteresis loops measured at different temperature further explore magnetic phase transitions as a function of external field and temperature. A possible phase diagram is similar to the previous Gd/Fe mult...