Domain Wall Roughness in Epitaxial FerroelectricPbZr0.2Ti0.8O3Thin Films

Abstract

The static configuration of ferroelectric domain walls was investigated using atomic force microscopy on epitaxial PbZr 0:2 Ti 0:8 O 3 thin films. Measurements of domain wall roughness reveal a power-law growth of the correlation function of relative displacements BL / L 2 with 0:26 at short length scales L, followed by an apparent saturation at large L. In the same films, the dynamic exponent was found to be 0:6 from independent measurements of domain wall creep. These results give an effective domain wall dimensionality of d 2:5, in good agreement with theoretical calculations for a twodimensional elastic interface in the presence of random-bond disorder and long-range dipolar interactions. DOI: 10.1103/PhysRevLett.94.197601 PACS numbers: 77.80.Dj, 68.37.Ps, 77.80.Fm, 77.84.Dy Understanding the behavior of elastic objects pinned by periodic or disorder potentials is of crucial importance for a large number of physical systems ranging from vortex lattices in type II superconductors [1], charge density waves [2], and Wigner crystals [3] to interfaces during growth [4] and fluid invasion [5] processes, and magnetic domain walls [6]. Ferroelectric materials, whose switchable polarization and piezoelectric and pyroelectric properties make them particularly promising for applications such as nonvolatile memories [7,8], actuators, and sensors [9], are another such system. In these materials, regions with different symmetry-equivalent ground states characterized by a stable remanent polarization are separated by elastic domain walls. The application of an electric field favors one polarization state by reducing the energy necessary to create a nucleus with polarization parallel to the field, and thereby promotes domain wall motion. Since most of the proposed applications use multidomain configurations, understanding the mechanisms that control domain wall propagation and pinning in ferroelectrics is an important issue.A phenomenological model derived from measurements of domain growth in bulk ferroelectrics [10 -12] initially suggested that the domain walls were pinned by the periodic potential of the crystal lattice itself. Such pinning was deemed possible because of the extreme thinness of ferroelectric domain walls (different from the case of magnetic systems). However, measurements of the piezoelectric effect [13], dielectric permittivity [14], and dielectric dispersion [15] in ferroelectric ceramics and sol-gel films have shown some features that cannot be described by the existing phenomenological theories. A microscopic study of ferroelectric domain walls could resolve these issues. Recently, we have measured domain wall velocity in epitaxial PbZr 0:2 Ti 0:8 O 3 thin films, showing that in this case commensurate lattice pinning is in fact not the dominant mechanism [16,17]. Rather, a creeplike velocity (v) response to an externally applied electric field E was observed with v expÿC=E , where C is a constant. The exponent characterizing the dynamic behavior of the system is a function of the domain wall dim...

Nonsteady relaxation and critical exponents at the depinning transition

“…(a) First, as is customary, we use the corrected expressions (19) and (20) to extract (ζ /z) and (β/νz), respectively. The fit should be performed above the microscopic regime t > t mic .…”

High-Resolution Studies of Domain Switching Behavior in Nanostructured Ferroelectric Polymers

“…44 The obtained D value is lower than that reported for BiFeO 3 and Pb(Zr,Ti)O 3 films, which can be explained if one assumes that the correlation length in polymer PVDF-TrFE nanomesas is shorter in comparison to solid-state crystalline ferroelectrics. 45,46 Further insight into the disorder potential has been obtained by mapping the spatial distribution of the local switching parameters using the DART-PFM mode ( Figure 5). 47 This method involves point-by-point acquisition of the local hysteresis loops over a grid of 20 × 20 points on the surface area of 300 × 300 nm 2 (Figure 5a,b).…”

Finite-temperature crossovers in periodic disordered systems

“…Typically these are divided into two categories. One encompasses interfaces in magnetic [2,3], ferroelectric [4,5] materials or spintronic systems [6], fluid invasion in porous media [7] and fractures [8,9]. The second concerns random periodic systems such as charge-density waves [10], vortex lattices in type II superconductors [11] and Wigner crystals [12].…”