Preparation of all-oxide ferromagnetic/ferroelectric/ superconducting heterostructures for advanced microwave applications

Abstract

As candidates for functional layers, 3d transition metal oxides with perovskite structures show some interesting properties, such as ferromagnetism, ferroelectricity and superconductivity. Accordingly, combinations of these properties can be used to create new tunable microwave devices. Ferromagnetic/ferroelectric/superconducting multistructures, such as La_0.70Sr_0.30MnO₃ (LSMO)/Pb(Zr_0.52Ti_0.48)O₃ (PZT)/YBa₂Cu₃O_7-y (YBCO) and YBCO/PZT/LSMO, have been fabricated by ArF excimer laser deposition on LaSrGaO₄ (LSGO) [001] and (La_0.30Sr_0.70)(Al_0.65Ta_0.35)O₃ (LSAT) [001] substrates. The resulting trilayer films have a highly c-axis oriented structure. Epitaxial YBCO films formed on PZT/LSMO//LSAT have a zero-resistance temperature of 87 K. Moreover, D-E and M-H hysteresis loop are observed for the LSMO/PZT/YBCO//LSGO structure using a conventional Sawyer-Tower circuit and a superconducting quantum interference device (SQUID). The remanent polarization and coercive field of the PZT layer are found to be 19 µC cm^-2 and 275 kV cm^-1 at 70 K, respectively. The remanent magnetic moment and coercive magnetic field are about 2.6 µ_B/site and 50 Oe respectively at 78 K. Furthermore, the microwave surface resistance (R_S) (22 GHz) of the YBCO film in the YBCO/PZT/LSMO structure was 1.32 m at 77 K. These results suggest that LSMO/PZT/YBCO structures are favourable for use in superconducting microwave applications such as tunable phaseshifters and filters.