The stability of the “T-like” (T′) phase in BiFeO3 films grown on LaAlO3(001) is investigated. We show that the T′ phase can be stabilized for thicknesses >70 nm under ultralow incident flux conditions in pulsed laser ablation growth. This low flux results in a low growth rate; thus, the sample is held at high temperatures (>600 °C) for much longer than is typical. Transmission electron microscopy and X-ray diffraction analysis suggest that such growth conditions favor the formation of nanoscale “defect pockets”, which apply a local compressive strain of ∼1.8%. We propose that the cumulative effect of local stresses induced by such “designer defects” maintains macroscale strain coherence mechanical boundary conditions, which then preserves the T′ phase to thicknesses beyond conventional wisdom. Finally, by intentionally introducing an amorphous phase at the film-substrate interface, it is shown that the mixed-phase proportion can be tuned for a given thickness.
We report on the magnetic and magnetodielectric behavior of epitaxial (001) transition metal oxide spinel iron vanadate (Fe 1+x V 2-x O 4 -FVO) thin films grown on (001) SrTiO 3 substrates by pulsed laser deposition. X-ray absorption spectroscopy (XAS) studies confirm the trivalent and nominally divalent nature of V and Fe ions, respectively, whilst an excess of Fe 3+ ions was also found. Aberrationcorrected cross-sectional scanning transmission electron microscopy analysis suggests that the excess Fe 3+ may be accommodated through Fe 3 O 4 stacking faults along the {111} planes. Temperaturedependent X-ray magnetic circular dichroism (XMCD) spectra revealed an anti-parallel alignment of spins between the Fe 2+ and V 3+ cations. M-H loops acquired at 10 K, well below the non-collinear ferromagnetic phase transition temperature, show magnetic anisotropy and point to the existence of two distinct phases with different coercive fields. Visual evidence for magnetic domains and their switching is given by magnetic force microscopy, which finds a switching field of ~ 3 T in agreement with the M-H loops. Magnetodielectric measurements for a Pd/FVO/Nb:STO heterostructure revealed a weak hysteresis in the magneto-capacitance loops at 10 K, thus confirming magneto-dielectric coupling. Detailed temperature and frequency dependent dielectric studies found that Maxwell-Wagner-type relaxation dominates capacitance behaviour above ~ 40 K due to a FVO/Nb:SrTiO 3 Schottky interface.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))
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