The transport physics of domain wall conductivity in La-doped bismuth ferrite (BiFeO3) 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.

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A new orthorhombic phase of the multiferroic BiFeO3 has been created via strain engineering by growing it on a NdScO(3)(110)(o) substrate. The tensile-strained orthorhombic BiFeO3 phase is ferroelectric and antiferromagnetic at room temperature. A combination of nonlinear optical second harmonic generation and piezoresponse force microscopy revealed that the ferroelectric polarization in the orthorhombic phase is along the in-plane {110}(pc) directions. In addition, the corresponding rotation of the antiferromagnetic axis in this new phase was observed using x-ray linear dichroism.

A new paradigm of domain wall nanoelectronics has emerged recently, in which the domain wall in a ferroic is itself an active device element. The ability to spatially modulate the ferroic order parameter within a single domain wall allows the physical properties to be tailored at will and hence opens vastly unexplored device possibilities. Here, we demonstrate via ambient and ultrahigh-vacuum (UHV) scanning probe microscopy (SPM) measurements in bismuth ferrite that the conductivity of the domain walls can be modulated by up to 500% in the spatial dimension as a function of domain wall curvature. Landau-Ginzburg-Devonshire calculations reveal the conduction is a result of carriers or vacancies migrating to neutralize the charge at the formed interface. Phase-field modeling indicates that anisotropic potential distributions can occur even for initially uncharged walls, from polarization dynamics mediated by elastic effects. These results are the first proof of concept for modulation of charge as a function of domain wall geometry by a proximal probe, thereby expanding potential applications for oxide ferroics in future nanoscale electronics.

In complex, correlated oxides, heterointerfaces have emerged as key focal points of current condensed matter science. [1][2][3] For ferroic oxides, in order to minimize the total energy, domain walls emerge as natural interfaces. Multiferroic materials show a wealth of controllable multiple ferroic order through stress, optical excitation, electric, or magnetic fi elds in the same phase, which in turn suggest potential applications in the realization of oxide-based electronic devices, such as spintronics, information storage devices, or communications. [4][5][6][7] According to the detailed classifi cation given by Mermin in ferroic systems, [ 8 ] domain walls in ferroic systems are considered as two dimensional (2D) topological defects, which play an important role in determining the functionality in materials with long-range order.Recently, several key studies pointed out interesting observations on domain walls in multiferroics. [9][10][11][12][13] For example, Y. Tokunaga et al. showed that ferroelectric polarization and magnetization are successfully controlled by magnetic and electric fi elds in GdFeO 3 , respectively, which is attributed to the unique feature of composite domain wall clamping. [ 14 ] T. Choi et al. observed insulating interlocked ferroelectric and structural antiphase domain walls in a multiferroic YMnO 3 system. [ 15 ] H. Bea et al. pointed out that domain walls are the source of the exchange bias interaction between the ferromagnetic metal layer and multiferroic BiFeO 3 (BFO). [ 16 ] Additionally, L. W. Martin further confi rmed that as-grown 109 ° domain walls in BFO thin fi lms are the contribution for uncompensated spins. [ 17 ] In addition to the above, a very recent work has established electrical conductivity at written multiferroic domain walls in BFO at room temperature, which opens up a pathway by which to manipulate domain walls for next generation nanoelectronics.Exploring details on electronic states of domain polarization reorientations is critical in oxide multiferroic materials. Theoretically, the consideration of the evolution of the polarization across the 109 ° domain walls exhibits a large potential step. The prediction correlates with the enhanced electrical conductivity due to the generation of a space-charge layer for screening the potential discontinuity in the region of the wall. [ 2 ] Experimentally, conductive atomic force microscopy (c-AFM) studies show the occurrence of electrical conduction at 109 ° domain walls within the limited spatial resolution of the experimental technigue. [ 3 ] In spite of the critical importance of these discoveries at such an oxide interface, there have been no effectively direct investigations of the intrinsic evolution of the electronic properties at regions of domain walls specifi cally within the nanoscale.In this work, we explore the subject by measuring the local electronic structure using scanning tunneling microscopy (STM) in a cross-sectional geometry. STM and scanning tunneling spectroscopy (STS) studies provide direct exp...