Domain Wall Roughness in Stripe PhaseBiFeO3Thin Films

Abstract

Using the model system of ferroelectric domain walls, we explore the effects of long-range dipolar interactions and periodic ordering on the behavior of pinned elastic interfaces. In piezoresponse force microscopy studies of the characteristic roughening of intrinsic 71 • stripe domains in BiFeO3 thin films, we find unexpectedly high values of the roughness exponent ζ = 0.74 ± 0.10, significantly different from those obtained for artificially written domain walls in this and other ferroelectric materials. The large value of the exponent suggests that a random field-dominated pinning, combined with stronger disorder and strain effects due to the step-bunching morphology of the samples, could be the dominant source of pinning in the system. [6]. Ferroelectric domain walls provide a useful model system in which many aspects of such glassy behavior can be readily accessed [7]. Previous studies of roughening, nonlinear dynamics, and aging have focused primarily on individual domain walls in uniaxial materials [8]. However, a particularly interesting experimental and theoretical challenge is posed by systems where coupled ferroic orders (such as ferroelectricity and ferroelasticity, or ferroelectricity and (anti)ferromagnetism [9]), as well as long-range interactions could lead to morecomplex behavior.Room-temperature multiferroic BiFeO 3 is an excellent candidate for investigating such phenomena. In this perovskite, polarization orientation along the eight pseudocubic [111] axes gives rise to three domain wall types (180 • , purely ferroelectric, and 71 • , 109 • , also ferroelastic), with magnetoelectric coupling between the ferroelectric and antiferromagnetic orders [10]. In addition, unusual domain wall functionalities [11,12] hold promise for future nanoelectronic applications [13,14]. BiFeO 3 films with specific polarization orientations, and domain structures ranging from nanoscale, sometimes fractallike "bubbles" to well-defined stripes can be obtained by adapting the deposition conditions and substrate [15][16][17]. Artificial domains can also be written by a biased scanning probe microscopy (SPM) tip, although this procedure can introduce significant electrochemical changes [18]. Intrinsic stripe domains follow standard LandauLifshitz-Kittel scaling of domain period w ∼ h 1/2 with the sample thickness h [19], while in samples with fractal bubble domains, a modified 0.59 exponent and apparent one-dimensional roughening of artificial domains were observed [20].Previous studies considered the domain walls as individual interfaces weakly pinned by disorder, with monoaffine roughness scaling characterized by a singlevalued roughness exponent ζ, dependent only on the disorder universality class and the system dimensionality. However, the heterogeneous disorder of ferroelectric thin films, with local universality class fluctuations and strong pinning [21], has recently been shown to lead to a breakdown of monoaffinity [22]. Moreover, in periodic systems interactions between neighboring interfaces can limit roughen...

Nanoscale studies of ferroelectric domain walls as pinned elastic interfaces

“…Even higher roughness exponent values of ζ = 0.7-0.8 were observed by Ziegler et al [112] for purely 71…”

Microwave a.c. conductivity of domain walls in ferroelectric thin films

“…To explain the large a.c. conduction of domain walls, we note that domain wall pinning by lattice defects, and associated strain and field disorder will disrupt the idealized straight shape of the wall making it locally curved 32 33 34 . The curvature in respect to polarization will translate into bound charges distributed along the roughened domain wall and compensated by localized clouds of mobile carriers, which are responsible for the enhanced a.c. conductivity.…”

From bulk descriptions to emergent interfaces: Connecting the Ginzburg-Landau and elastic-line models

“…Diverse systems including ferroic domain walls [1][2][3][4][5][6][7][8][9][10][11], cell fronts [12,13], bacterial colonies [14], or contact lines [15] exhibit emergent structures separating different "states" or domains (i.e., different magnetization orientations in the case of ferromagnetic systems, or different polarization orientations in the case of ferroelectrics, or cells-media in cell fronts, or wet from dry in the case of contact lines), usually called interfaces. From a technological point of view, controlling interfaces is of great interest for various reasons.…”