Shedding light on magnetoelectric coupling

Scanning electron microscopy image of the sample corresponding to a top view on the nanopillar structure.

Scanning electron microscopy image of the sample corresponding to a top view on the nanopillar structure. © Uni Duisburg

Effect opens up new possibilities for digital data storage


It is possible to control the electric properties of solids by magnetic fields by means of the so-called magnetoelectric coupling. This has been investigated by scientists from the University of Duisburg-Essen and the Institute for Complex Magnetic Materials of the HZB at the electron storage ring BESSY II. The effect can be used to develop new data storage media which are faster and more energy saving than today. The scientists published their results in the current issue of the journal “Nature Communications”.


Dr. Carolin Schmitz-Antoniak from the team of Prof. Heiko Wende at the University of Duisburg-Essen used a composite consisting of a few hundred nanometers long cobalt ferrite nanopillars embedded in a barium titanate matrix. The magnetostrictive nanopillars are deformed in an applied magnetic field, and the surrounding matrix is piezoelectric, i.e. it builds up an electric voltage under mechanical strain. The scientists deformed the nanopillars by applying a magnetic field and thereby created in this composite a mechanical stress to the matrix which finally exhibited an electric voltage.

The investigations, performed in collaboration with Dr. Detlef Schmitz from the Institute for Complex Magnetic Materials at BESSY II, proved successful. The experiments were performed with the high-field endstation at beamline UE46-PGM1 using also the unique possibility to rotate the high magnetic field relative to the direction of the incident soft x-ray radiation. Utilizing the combination of what is known as circular and linear dichroism, the scientists studied the magnetism and the electric polarization of the nanopillars and the matrix of the composite, respectively.

In addition, experiments with hard x-rays were performed in collaboration with Dr. Esther Dudzik and Dr. Ralf Feyerherm of the same HZB Institute at the MAGS beam-line. The resulting information about the crystal structure of the sample directly verified the deformation of the matrix by the applied magnetic field.

By analyzing all experimental results the researchers concluded how the electric polarization is controlled by magnetic fields. The effect is based on smallest deformations of the materials in the composite. If the magnetic field is applied along the longitudinal axis of the nanopillars, then the nanopillars shorten longitudinally. At the same time the nanopillars become thicker in order to conserve their volume. As a consequence the surrounding matrix is squeezed uniformly. In contrast, if the magnetic field is applied along a transverse axis of the nanopillars, then the nanopillars shorten along this axis whereas they expand at right angles to it. In this way the matrix is stretched along the magnetic field and compressed at right angles to it, resulting in an asymmetric polarization distribution which has not been observed in this system before.

The composite is relevant as a digital data storage medium because the electric polarization is maintained even when the magnetic field is switched off again. Therefore the researchers also developed a strategy to compress single nanopillars by electric current pulses along longitudinal and transverse axes to write information bitwise.

Read the paper in Nature communication: DOI: 10.1038/ncomms3051

IH


You might also be interested in

  • Fertilisation under the X-ray beam
    Science Highlight
    19.03.2024
    Fertilisation under the X-ray beam
    After the egg has been fertilized by a sperm, the surrounding egg coat tightens, mechanically preventing the entry of additional sperm and the ensuing death of the embryo. A team from the Karolinska Institutet has now gained this new insight through measurements at the X-ray light sources BESSY II, DLS and ESRF. 
  • Neutron experiment at BER II reveals new spin phase in quantum materials
    Science Highlight
    18.03.2024
    Neutron experiment at BER II reveals new spin phase in quantum materials
    New states of order can arise in quantum magnetic materials under magnetic fields. An international team has now gained new insights into these special states of matter through experiments at the Berlin neutron source BER II and its High-Field Magnet. BER II served science until the end of 2019 and has since been shut down. Results from data at BER II are still being published.

  • The future of BESSY
    News
    07.03.2024
    The future of BESSY
    At the end of February 2024, a team at HZB published an article in Synchrotron Radiation News (SRN). They describe the next development goals for the light source as well as the BESSY II+ upgrade programme and the successor source BESSY III.