Observation of an antiparallel magnetic state in Fe3O4/Mn3O4 superlattices

[Fe3O4(20 Angstrom)/Mn3O4(80 Angstrom)](x20) and [Fe3O4(20 Angstrom)/MgO(80 Angstrom)](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/cm(3), is observed only from the Fe3O4/Mn3O4 superlattice at temperature below similar to 60 K. This observation indicates that the magnetic moments in two constituents are antiparallel and the Curie temperature (T-c) of Mn3O4 is enhanced for 15 K. In addition, the remanent magnetization shows a compensation point (T-cp) 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 multilayered system in that Mn3O4 is parallel and Fe3O4 antiparallel to the applied field below T-cp while Fe3O4 is parallel and Mn3O4 antiparallel to the applied field above T-cp. Moreover, a spin-flop-like phase is observed above a critical external field, H*, similar to 10 kOe. (C) 2000 American Institute of Physics. [S0003-6951(00)00205-9].