Domain Wall Conductivity in La-Doped ${\mathrm{BiFeO}}_3$

The transport physics of domain wall conductivity in La-doped bismuth ferrite (${\mathrm{BiFeO}}_3$) has been probed using variable temperature conducting atomic force microscopy and piezoresponse force microscopy in samples with arrays of domain walls in the as-grown state. Nanoscale current measurements are investigated as a function of bias and temperature and are shown to be consistent with distinct electronic properties at the domain walls leading to changes in the observed local conductivity. Our observation is well described within a band picture of the observed electronic conduction. Finally, we demonstrate an additional degree of control of the wall conductivity through chemical doping with oxygen vacancies, thus influencing the local conductive state.

Figure 1

(a) PFM amplitude and (b) PFM phase images of a BFO sample with 109° stripe domains. (c) Simultaneously acquired $c$-AFM image of the same area showing that each 109° domain wall is electrically conductive.

Figure 2

(a) Several $I\mathrm{\text{−}}V$ curves measured by stepping the c-AFM tip perpendicular across a domain wall at 340 K. Data plotted in linear coordinates for Schottky emission. (b) Typical 3D plot of such a measurement; (c) same data as in (a) plotted in linear coordinates for Fowler-Nordheim tunneling.

Figure 3

(a) Histogram analysis, saturated peak value (blue), whole peak (red), and whole raw data (green) are extracted. (b) Typical histograms of $\log (I)$. (c) Current levels extracted from histogram analysis of $c$-AFM images at various temperatures and tip biases for the 500 Torr oxygen cooled sample and 100 mTorr oxygen cooled sample. The error bars are FWHM of the corresponding histograms. Activation energies are given in the inset.

Figure 4

(a) Schematic band diagram for the 109° domain wall. (b) Current levels extracted from histogram analysis of $c$-AFM images at room temperature for samples with different oxygen cooling pressure and thus varying density of oxygen vacancies.