Narrow Results

Bi₂FeCrO₆ thin films were epitaxially grown by pulsed laser deposition on (100)-oriented LaAlO₃, (LaAlO₃)_0.3(Sr₂LaTaO₆)_0.7 and SrTiO₃ single crystalline substrates with and without epitaxial CaRuO₃ buffered layer. The in-plane compressive strain induces monoclinic distortion of the Bi₂FeCrO₆ lattice cell. The strain originates from lattice mismatch between CaRuO₃ and single crystal substrates. The similar crystal structure of the substrate and the layer lead to coherent epitaxial growth of the heterostructures and avoid strain relaxation in particular for BFCO films deposited on LaAlO₃ substrates. The ferroelectric character is demonstrated for all grown BFCO films. The residual in-plane strain weakly affects the effective piezoelectric coefficient of BFCO layers.

Pb(Zr_0.65Ti_0.35)O₃ (PZT) thin films were deposited on SrRuO₃ (SRO) buffer layer coated LaAlO₃ (LAO) substrates by RF sputtering method. X-ray diffraction analyses indicate that the PZT thin films show epitaxial orientation and the in-plane epitaxial relationship between film and substrate is deduced as (001)[010]_PZT‖(001)[010]_SRO‖(001)[010]_LAO. Despite the Zr-richcomposition, observations using transmission electron microscopy reveal that the PZT thin films exhibited tetragonal phase, which was due to the clamping effect of the substrates. The clamping effecton the electrical properties, especially on the dielectric properties, was evaluated. Ferroelectric measurements show that PZT films with LAO/SRO substrates were fatigue-free. However, the test of dielectric property dependences on temperature manifests a relatively low Curie temperature of the PZT films. The loss tangent decreasedwith increase intemperature. Owing to the release of clamping stress, the loss tangent decreased dramatically while the temperature was approaching the phase transition temperature of PZT thin films.

Ability of epitaxial perovskite oxide ferroelectric films to maintain a poled polarization state on a long-term scale is crucial for advanced devices employing such films. Here polarization relaxation with time, or aging, is experimentally studied in epitaxial capacitor heterostructures of PbTiO₃ sandwiched between SrRuO₃ and Pt electrodes. The relaxation obeys logarithmic time-decay for the time 10²–10⁵s after poling pulses. The decay is by factor $\sim$10 slower than that reported for polycrystalline films. Our experimental results show that existing models are insufficient for epitaxial films.

The cubic polymorph of the binary transition metal pnictide (TMP) MnSb, c-MnSb, has been predicted to be a robust half-metallic ferromagnetic (HMF) material with minority spin gap ≳1 eV. Here, MnSb epilayers are grown by molecular beam epitaxy (MBE) on GaAs and In_0.5Ga_0.5As(111) substrates and analyzed using synchrotron radiation X-ray diffraction. We find polymorphic growth of MnSb on both substrates, where c-MnSb co-exists with the ordinary niccolite n-MnSb polymorph. The grain size of the c-MnSb is of the order of tens of nanometer on both substrates and its appearance during MBE growth is independent of the very different epitaxial strain from the GaAs (3.1%) and In_0.5Ga_0.5As (0.31%) substrates.

The D0${}_{22}$–Mn₃Ga ferrimagnet promises potential applications in spintronics due to its low magnetization, strong perpendicular magnetic anisotropy and high Curie temperature. In the form of thin and thick films, these properties are preserved. Here, we report on the structural and magnetic characterization of epitaxial D0${}_{22}$–Mn${}_{2.6}$Ga ultrathin films with thicknesses of 2nm, 5nm and 8nm grown on Cr buffer layers by magnetron sputtering. We found that the films are perfect single crystals with flat surfaces and Curie temperatures higher than 300K. The 2nm-thick ultrathin film has higher magnetization than that of the thicker films, likely due to uncompensated ferrimagnetic planes, along the c-axis, linked to the surface roughness at the atomic scale. These properties highly suit the requirements for the elaboration of spintronic devices such as magnetic tunnel junctions.