Large Carrier Mobilities in ErMnO₃ Conducting Domain Walls Revealed by Quantitative Hall-Effect Measurements

Abstract

Kelvin probe force microscopy (KPFM) has been used to directly and quantitatively measure Hall voltages, developed at conducting tail-to-tail domain walls in ErMnO single crystals, when current is driven in the presence of an approximately perpendicular magnetic field. Measurements across a number of walls, taken using two different atomic force microscope platforms, consistently suggest that the active p-type carriers have unusually large room temperature mobilities of the order of hundreds of square centimeters per volt second. Associated carrier densities were estimated to be of the order of 10 cm. Such mobilities, at room temperature, are high in comparison with both bulk oxide conductors and LaAlO-SrTiO sheet conductors. High carrier mobilities are encouraging for the future of domain-wall nanoelectronics and, significantly, also suggest the feasibility of meaningful investigations into dimensional confinement effects in these novel domain-wall systems.

Domains and domain walls in multiferroics

“…This abundance is due to the fact that multiferroics are often improper ferroelectrics (see Section 1 and 2), where the formation of domains is governed by, e.g., a structural or magnetic order parameter and not the electric polarization [40]. Multiferroic hexagonal manganites, RMnO 3 , exhibit an intriguing ferroelectric domain pattern [106,116] and are an interesting example for the natural emergence of both neutral [106,117] and charged domain walls [57,105,[118][119][120][121]: Here, a trimerizing lattice distortion leads to stable 180°charged domain walls with anomalous electronic transport properties (Figure 6(a), (b)) [105,119]. The extraordinary stability of these charged domain walls is reflected by recent electrostatic force microscopy measurements [122], which showed that partially unscreened walls arise at low temperature, representing a rare example of a stable, electrically uncompensated oxide interface (Figure 6(c)).…”

Domain wall-localized phonons in BiFeO3: spectrum and selection rules

“…The seminal work of Seidel et al 1 demonstrated that DC conductivity is higher at domain walls (DWs) in BiFeO 3 (BFO) than in the bulk, enabling signal transmission along the walls. This inspired a new paradigm for the design of DW-based nanoelectronic devices 2,3,[4][5][6][7][8][9][10][11][12] , leading to the demonstration of DW-based diode and transistor operating in kHz range 6,12 . The push for higher frequencies [13][14][15] , used in modern computers, has led to a discovery of giant increase of the effective DW conductivity at GHz frequencies in recent microwave microscopy experiments 15,16,17 .…”

An Electronically Driven Improper Ferroelectric: Tungsten Bronzes as Microstructural Analogs for the Hexagonal Manganites

“…The aspiration is that these 2D-'sheet'-materials could therefore be exploited in new forms of agile nano-electronics [4] . Emergent electrical properties of DWs include enhanced or diminished electrical conductivity (both ac and dc) in a wide range of materials including BiFeO3, [5,6] BaTiO3, [7,8] LiNbO3, [9] PZT [10] , KTP [11] , copper-chloride boracites [12] and members of the rare earth manganites (RMnO3, R = Y, Er, Ho) [13][14][15][16][17] . The ambition to exploit DWs with different functionality for nano-electronics, however, stretches beyond simply reconfigurable circuitry which relies on DW conduction to direct current.…”

“…The improper ferroelectric [20] rare earth manganites, RMnO3 (R 3+ = Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc), in particular have generated widespread interest as the geometrically-driven improper nature of ferroelectricity results in striking six-domain 'cloverleaf' vertices linked by labyrinthine (meandering) DWs with wide-ranging functionalities [13,[15][16][17] . Specifically the domain microstructure involves interlocking of (structural) antiphase and ferroelectric boundaries [21] to produce the labyrinthine domain structures with six-domain vertices rather than conventional stripe or "tweed" patterns.…”

“…The meandering nature of the domain walls, coupled with the uniaxial polarisation in the system, guarantees that sections of the domain walls will support polarisation discontinuities. In many of the rare-earth manganites, such discontinuities have been associated with enhanced conductivity measured both through conducting atomic force microscopy (cAFM) [13][14][15]44] and localised Hall Effect [16,45] measurements. Initial investigations using cAFM did not reveal enhanced conduction at domain walls in CsNbW2O9, but it is unclear that a percolative pathway from the conducting AFM tip to the electrical earth at the base of the ceramic sample had been established.…”