Séminaire DQMP

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Date(s) - 24/03/2015
13 h 00 min - 14 h 00 min

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Auditoire Stückelberg – Ecole de physique

 

Ferroelectric domain dynamics under controlled strain

Kathrin Dörr

 

1 MLU Halle-Wittenberg, Institute for Physics, 06099 Halle, Germany

2 IFW Dresden, 01171 Dresden, Germany

 

Domain wall motion governs the speed of ferroelectric switching, since switching without do-main walls is not yet confirmed for any ferroelectric. It is thus of strong fundamental as well as practical interest. Nucleation and domain wall motion in ferroelectrics have originally been studied in crystals [1] and, more recently, in thin films by piezoresponse force microscopy (PFM) [2]. Crystallographic defects and electrode interfaces have been found to play a deci-sive role as nucleation and pinning centers. On the other hand, the elastic strain present in thin epitaxial films was recently utilized to control the remanent polarization or the stable domain pattern or even to induce ferroelectricity and multiferroicity. Based on the strong coupling of strain and ferroelectricity, one also expects a substantial influence of domain dynamics, which was hard to investigate experimentally because of the difficulty to vary the elastic strain in a single sample with fixed microstructure. We contribute in filling this gap by introducing a reversibly strained piezoelectric thin film substrate to force microscopy [3].

 

After observing the strain-dependent switching time of BiFeO3 and PbZr0.48Ti0.52O3 capaci-tors in earlier work, we developed an approach for PFM in controlled strain states of the ferroelectric film in order to access the nanoscopic domain processes. Epitaxial single-domain films of PbZr0.2Ti0.8O3 on piezoelectric substrates of 0.72PbMg1/3Nb2/3O3-0.28PbTiO3(001) (PMN-PT) covered with a conducting oxide electrode can be biaxially and reversibly compressed by ≤0.13 % in ambient conditions. The lateral velocity of domain walls has been determined from the diameters of remanent domains [2]. Besides a strain-dependent relaxation of the remnant domain radius, we find a strain dependence of the activation field for wall motion which can reversibly alter the creep velocity in small fields by orders of magnitude. Known mechanisms for wall motion have been scrutinized for an explanation of the strain effect. As one origin, the built-in field of the Schottky contact between bottom electrode and ferroelectric has been found to be sensitive to strain (as can be measured in switching spectroscopy maps). Since this mechanism cannot completely explain the observations, we consider the option of strain-controlled depolarizing charges on (tilted sections of) domain walls [3].

 

[1]  R. C. Miller and A. Savage, J. Appl. Phys. 31, 662 (1960)

[2]  T. Tybell, P. Paruch, T. Giamarchi, and J.-M. Triscone, Phys. Rev. Lett. 89, 097601 (2002)

[3]  E.-J. Guo, R. Roth, A. Herklotz, D. Hesse, K. Dörr, Adv. Mat., DOI: 10.1002/adma.201405205

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