(a) High angle X-ray diffraction spectra for a series of BFO(∼30 nm)/YBCO(n u.c.)/PBCO(2.4 nm) heterostructures on STO, for YBCO thickness n = 6, 5, 3, and 1 u.c. (from top to bottom). The (0 0 n) peaks of YBCO/PBCO and BFO are marked with dotted and full lines, respectively. The inset shows the rocking curve around the (001) BFO reflection for a BFO(30 nm)/YBCO(6 u.c)/PBCO(4 u.c.) sample. (b) Low-angle X-ray diffraction spectra for the same series of samples. The solid lines are the best fits using the SUPREX model. 21 The inset shows the rocking curve around the (005) YBCO/PBCO reflection for a BFO(30 nm)/YBCO(6 u.c)/PBCO(4 u.c.) sample. (c) Zoom of some of the curves shown in (a). The main panel displays the X-ray diffraction spectrum around the (001) BFO reflection for the 3 u.c YBCO heterostructure (solid line), which shows finite size oscillations. The dashed line is the theoretical Laue pattern for a 27 nm thick BFO films (c-axis parameter 0.407 nm), in good agreement with the nominal thickness (30 nm). The inset shows a zoom around the (005) PBCO/YBCO reflection for the samples with YBCO thickness 1, 3, and 5 unit cells (from bottom to top). The arrows point the finite size oscillations. (d) BFO and YBCO/PBCO c-axis parameter as a function of the YBCO thickness, calculated from the series of HAXRD spectra shown in (a). The c-axis parameters expected for thin PBCO films on STO and for thick YBCO films on STO (taken from Ref. 20 ) are marked with horizontal lines.
All measurements for a BFO(30 nm)/YBCO(3 u.c.)/PBCO//STO heterostructure. (a) Topography, (b) out-of-plane phase, and (c) in-plane phase after artificially writing a 500 × 500 nm2 ferroelectric domain (dark contrast in (b)). (d) CTAFM resistance mapping of BFO and (e) histogram of the resistance over the scanned area. The inset shows a local I(V) curve measured with the CTAFM.
Resistance versus temperature of BFO(30 nm)/YBCO (n u.c.)/PBCO(2.4 nm)//STO with YBCO layers with thicknesses n from 1 u.c. to 6u.c.
Resistance versus temperature for a BFO(30 nm)/YBCO (4 u.c.)/PBCO(2.4 nm)//STO heterostructure in the “as-grown” state (a), and after subsequently reversing the ferroelectric polarization outwards (b), towards (c), and outwards (d) the YBCO layer. The sketch indicates the direction of the ferroelectric polarization and the expected variation in the carrier density within the YBCO layer.
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