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. 2013:4:1534.
doi: 10.1038/ncomms2548.

Magnetic switching of ferroelectric domains at room temperature in multiferroic PZTFT

D M Evans  1 , A Schilling, Ashok Kumar, D Sanchez, N Ortega, M Arredondo, R S Katiyar, J M Gregg, J F Scott
Affiliations
Free PMC article

Magnetic switching of ferroelectric domains at room temperature in multiferroic PZTFT

D M Evans et al. Nat Commun. 2013.
Free PMC article

Abstract

Single-phase magnetoelectric multiferroics are ferroelectric materials that display some form of magnetism. In addition, magnetic and ferroelectric order parameters are not independent of one another. Thus, the application of either an electric or magnetic field simultaneously alters both the electrical dipole configuration and the magnetic state of the material. The technological possibilities that could arise from magnetoelectric multiferroics are considerable and a range of functional devices has already been envisioned. Realising these devices, however, requires coupling effects to be significant and to occur at room temperature. Although such characteristics can be created in piezoelectric-magnetostrictive composites, to date they have only been weakly evident in single-phase multiferroics. Here in a newly discovered room temperature multiferroic, we demonstrate significant room temperature coupling by monitoring changes in ferroelectric domain patterns induced by magnetic fields. An order of magnitude estimate of the effective coupling coefficient suggests a value of ~1 × 10(-7) sm(-1).

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Figures

Figure 1
Figure 1. Complex domain structures in PZTFT single crystal.
Scanning transmission electron microscopy (STEM) reveals a rich microstructure in which domains form into irregular patterns, with domain walls that do not obviously adhere to strict crystallographic orientations (a). Despite this complexity, it seems that all the domain variants have formed from a single higher symmetry parent state, as the selected area diffraction patterns from different regions, indicated by the coloured circles in (b), are indistinguishable. Scale bar, 200 nm.
Figure 2
Figure 2. Ferroelectric domain configurations changing dramatically with an applied magnetic field.
Lateral piezoresponse force microscopy (LPFM) images, before (a) and after (b) the application of a 18-kOe magnetic field, show obvious changes in ferroelectric domain states. In both (a,b) the same region of the PZTFT single-crystal lamella has been scanned. In each case, the left and middle panels are amplitude images, showing variations in the local in-plane piezoelectric activity, with the cantilever orientation in each scan given by the blue schematic tip shape. The directions of tip distortion contributing to the amplitude images are given by the black arrows superposed onto the schematic cantilevers. Domains or packets of domains are clearly distinguished. The right panels are simple in-plane vector maps of the local polarization direction, inferred from the phase signal associated with the amplitude images presented in the middle and left panels. Polar directions are assigned to one of four quadrant directions (grey: left and up; lime green: left and down; purple: right and up; brown: right and down). The magnetic field has caused obvious growth in the domains with polar orientations represented by the lime green colour. Scale bar, 2 μm.
Figure 3
Figure 3. Modest magnetic fields induce partially reversible changes in ferroelectric domains.
Phase images from lateral piezoresponse force microscopy (LPFM) change depending on the orientation of the magnetic field applied to the PZTFT lamella. Both the images in (a) and the area histograms of different phase colours (b) illustrate that 3 kOe applied in a nominally positive direction, perpendicular to the lamellar surface, favours the growth of polarization directions indicated by red contrast. When applied in a nominally negative direction, these regions contract. Scale bar, 2  μm.
Figure 4
Figure 4. Transmission electron microscopy shows distinct changes in domain microstructure induced by magnetic fields.
The same region of the sample was imaged (dark field 1–10pc reflection; zone axis <110>pc) before (a) and after (b) the application of a magnetic field of 3 kOe perpendicular to the sample surface. The region imaged in (a) was characterized by bundles of fine-scale domains (c), commensurate with Fig. 1. However, quite dramatic changes to coarser ‘labyrinthine’ or ‘maze’ domains, (b,d), were found after exposure to the magnetic field. In (a,b) scale bar, 500 nm; in (c,d) scale bar, 50 nm.
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