Spin- and charge-modulated trilayer magnetic junctions: La_0.7Ca_0.3MnO₃/La_0.45 Ca_0.55MnO₃/La_0.7Ca_0.3 MnO₃

We report on magnetic tunnel junctions entirely made up of mixed-valence manganites, La_0.7Ca_0.3MnO₃/La_0.45 Ca_0.55MnO₃/La_0.7Ca_0.3 MnO₃. In heteroepitaxial junctions, the different Mn³⁺/Mn⁴⁺ mixed-valence ratios can modulate the ground states throughout the trilayer, i.e. ferromagnetic metal/antiferromagnetic insulator/ferromagnetic metal. Interestingly, the tunnel magnetoresistance (TMR) of the device persists up to a higher temperature (T/T_c ≤ 0.75, where T_c is the Curie temperature) as compared to the case for equivalent non-manganite barrier junctions. The enhanced TMR at high temperatures in the present junction is discussed in relation to the properties of the unique interface between the metallic ferromagnet and the antiferromagnetic tunnel barrier, such as the interfacial bonding coherence and a magnetic interlayer coupling.