Electrical Switching of Magnetic Polarity in a Multiferroic ${\mathrm{BiFeO}}_{3}$ Device at Room Temperature

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Electrical Switching of Magnetic Polarity in a Multiferroic ${BiFeO}_{3}$ Device at Room Temperature

N. Waterfield Price, R. D. Johnson, W. Saenrang, A. Bombardi, F. P. Chmiel, C. B. Eom, and P. G. Radaelli

Phys. Rev. Applied 8, 014033 – Published 27 July 2017

Abstract

We have directly imaged reversible electrical switching of the cycloidal rotation direction (magnetic polarity) in a $(111)_{pc} − {BiFeO}_{3}$ epitaxial-film device at room temperature by nonresonant x-ray magnetic scattering. Consistent with previous reports, fully relaxed $(111)_{pc} − {BiFeO}_{3}$ epitaxial films consisting of a single ferroelectric domain are found to comprise a submicron-scale mosaic of magnetoelastic domains, all sharing a common direction of the magnetic polarity, which is found to switch reversibly upon reversal of the ferroelectric polarization without any measurable change of the magnetoelastic domain population. A real-space polarimetry map of our device clearly distinguishes between regions of the sample electrically addressed into the two magnetic states with a resolution of a few tens of micron. Contrary to the general belief that the magneto-electric coupling in ${BiFeO}_{3}$ is weak, we find that electrical switching has a dramatic effect on the magnetic structure, with the magnetic moments rotating on average by 90° at every cycle.

Received 29 March 2017

DOI:https://doi.org/10.1103/PhysRevApplied.8.014033

Physics Subject Headings (PhySH)

Ferroelectricity Magnetic order Magnetic texture Magnetization switching Multiferroics

Devices Noncollinear magnets Oxides

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

N. Waterfield Price^1,2,*, R. D. Johnson^1,3, W. Saenrang⁴, A. Bombardi², F. P. Chmiel¹, C. B. Eom⁴, and P. G. Radaelli¹

¹Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
²Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot OX11 0DE, United Kingdom
³ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom
⁴Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA

^*noah.waterfieldprice@physics.ox.ac.uk

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Vol. 8, Iss. 1 — July 2017

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Figure 1
Magnetic polarity. (a), (b) Magnetic spin cycloids of opposite magnetic polarity.
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Figure 2
$(111)_{pc} − BFO$ film device. (a) Photograph of the $(111)_{pc} − BFO$ film. (b) Optical microscope image of the $(111)_{pc} − BFO$ film surface. Maps of the magnetic polarity (see Fig. 5) are overlaid showing regions of the sample switched into the $FE ↓$ and $FE ↑$ state and the direction of the FE polarization is shown by the white symbols. (c) polarization–electric-field ( $P − E$ ) hysteresis-loop measurement.
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Figure 3
Nonresonant magnetic x-ray scattering experimental setup. The incident and scattered x-ray beam directions are indicated by the blue arrows. The incident x rays are linearly polarized with their $E$ -field vector perpendicular to the scattering plane ( $σ$ polarized). These may be converted to circularly polarized x rays of either handedness using a diamond phase plate. The polarization of the scattered x rays is measured using a graphite analyzer crystal which can be rotated to select any linear polarization channel.
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Figure 4
Magnetic diffraction reciprocal space maps. (a), (b) NXMS reciprocal space maps about $(009)_{h}$ with left-circular and right-circular polarized light, respectively, in the virgin $FE ↓$ state. (f), (g) Fitted NXMS reciprocal space maps about $(009)_{h}$ with left-circular and right-circular polarized light, respectively, in the virgin $FE ↓$ state. (d), (e) NXMS reciprocal space maps about $(009)_{h}$ , with left-circular and right-circular polarized light, respectively, in the switched (nominally) $FE ↑$ state. (i), (j) Fitted NXMS reciprocal space maps about $(009)_{h}$ with left-circular and right-circular polarized light, respectively, in the switched (nominally) $FE ↑$ state. (c) Schematic showing the effect of the monoclinic distortion on the diffracted signal, showing the undistorted (translucent) and distorted (opaque) diffraction patterns. (h) FE polarization of the sample measured while switching into the $FE ↑$ state. The points at which the reciprocal space maps in (a), (b) and (d), (e) are measured are labeled with $↓$ and $↑$ , respectively. The black arrow indicates the electric-field sweep direction. (k), (l) The percentage fraction of both the $β = + 1$ and $β = - 1$ magnetic polarities of the measured regions. The scale bar in (c) shows the magnitude of the propagation vector (all reciprocal space maps on the same scale) and the reciprocal lattice directions (in the hexagonal setting) are indicated by the translucent black arrows on the reciprocal space maps. All measurements are taken at room temperature.
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Figure 5
Real-space maps. (a) Magnetic polarity real-space map of an area of the sample containing regions that have been switched into the $FE ↑$ state. The white dotted circle in the lower left corner indicates the spatial resolution of the measurement. (b) Magnetic polarity real-space map of an area of the sample containing regions that have been switched into the $FE ↑$ state and then switched back into the $FE ↓$ state. The regions underlying the Pt electrodes are outlined by the white solid lines, and the surrounding regions are in the virgin $FE ↓$ state. The scale and color bars refer to both (a) and (b). Based upon the characterization of switched and unswitched regions shown in Fig. 4, a dichroic asymmetry of $+ 0.4$ and $- 0.4$ corresponds to a magnetic polarity of $β = - 1$ and $β = + 1$ , respectively. $x$ and $y$ are two orthogonal directions that describe the lateral sample translation. These maps have been overlayed on an image of the sample in Fig. 2.
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Physical Review Applied

Electrical Switching of Magnetic Polarity in a Multiferroic BiFeO3 Device at Room Temperature

N. Waterfield Price, R. D. Johnson, W. Saenrang, A. Bombardi, F. P. Chmiel, C. B. Eom, and P. G. Radaelli

Phys. Rev. Applied 8, 014033 – Published 27 July 2017

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Electrical Switching of Magnetic Polarity in a Multiferroic ${BiFeO}_{3}$ Device at Room Temperature