Locating the Elusive

 HZB staff scientist Florin Radu checks the BaTiO3 sample<br />alignment in the ALICE diffractometer.

HZB staff scientist Florin Radu checks the BaTiO3 sample
alignment in the ALICE diffractometer.

HZB scientists observe how a material at room temperature exhibits a unique property – a „multiferroic“ material with potential uses for cheap and quick data storage.

Researchers at Helmholtz-Zentrum Berlin (HZB) in close collaboration with colleagues in France and UK, have engineered a material that exhibits a rare and versatile trait in magnetism at room temperature. It’s called a “multiferroic,” and it means that the material has properties allowing it to be both electrically charged (ferroelectric) and also the ability to be magnetic (ferromagnetic), with its magnetisation controlled by electricity.

This research was based around a material known as barium titanate (BaTiO3), a ferroelectric crystal that is promising to have potential uses in multi-state data storage while being cost effective. Their paper titled, “Interface-induced room-temperature multiferroicity in BaTiO3” appears now in Nature Materials.

“We’ve shown a way where you can obtain a multiferroic at room temperature,” said Sergio Valencia, post doc researcher at HZB, referring to the scarcity of room temperature examples. “Barium titanate is ferromagnetic, so it means you have a net-magnetic moment you can really control by an electric field. The idea is that you can apply a voltage to the ferroelectric reversing the ferroelectric polarization which in turn affects the magnetization of your film [BaTiO3].

You can use this for example to write bits of information in memories of computers by only applying voltages, which is much cheaper in terms of power than traditionally applying magnetic fields.”

It is this ability to control the material’s magnetism and to be able to do it at room temperatures which makes this multiferroic potentially more cost-effective compared to other current multiferroic materials, which require complex arrangements to work.

Finding these two traits of ferromagnetic and ferroelectric working together in a compound is tricky due to the strange love-hate relationship exhibited by the two phenomena. What a ferromagnetic requires to exist is not the same as what a ferroelectric requires. Yet strangely, the two compliment each other and share a strong relationship, where one affects the other. The scarcity of these multiferroics however, is a result of this unique phenomenon combined with the few naturally occurring examples.  “They are scarce and the problem is that most of them are multiferroic only at very low temperatures,” added Valencia. “Therefore they are not useful for applications. If you have to go to  -270 °C for a multiferroic then it’s really complicated and expensive to implement them in room temperature working devices.”

The researchers witnessed this multiferroic behaviour by investigating magnetic moments of Titanium (Ti) and Oxygen (O) atoms in BaTiO3  by using BESSY II synchrotron radiation source of Helmholtz-Zentrum Berlin.

They used a research method known as soft X-ray resonant magnetic scattering. The team was able to witness the dual traits of both ferroelectric and ferromagnetic in the thin films of BaTiO3. And since BaTiO3 is a non-magnetic ferroelectric material at room temperature, the ferromagnetism was induced by proximity to natural ferromagnets such as iron (Fe) and Cobalt (Co). In order to achieve these results the researchers deposited a ten atom thin film of iron and cobalt on top of a four atom thin BaTiO3 film. “These small thicknesses are indeed required for the implementation of such materials in devices to keep their small size,” added Valencia.

Eric Verbeten


You might also be interested in

  • 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.

  • Spintronics: X-ray microscopy unravels the nature of domain walls
    Science Highlight
    28.08.2023
    Spintronics: X-ray microscopy unravels the nature of domain walls
    Magnetic skyrmions are tiny vortices of magnetic spin textures. In principle, materials with skyrmions could be used as spintronic devices, for example as very fast and energy-efficient data storage devices. But at the moment it is still difficult to control and manipulate skyrmions at room temperature. A new study at BESSY II analyses the formation of skyrmions in ferrimagnetic thin films of dysprosium and cobalt in real time and with high spatial resolution. This is an important step towards characterising suitable materials with skyrmions more precisely in the future.
  • Spintronics at BESSY II: Domain walls in magnetic nanowires
    Science Highlight
    02.06.2023
    Spintronics at BESSY II: Domain walls in magnetic nanowires
    Magnetic domains walls are known to be a source of electrical resistance due to the difficulty for transport electron spins to follow their magnetic texture. This phenomenon holds potential for utilization in spintronic devices, where the electrical resistance can vary based on the presence or absence of a domain wall. A particularly intriguing class of materials are half metals such as La2/3Sr1/3MnO3 (LSMO) which present full spin polarization, allowing their exploitation in spintronic devices. Still the resistance of a single domain wall in half metals remained unknown. Now a team from Spain, France and Germany has generated a single domain wall on a LSMO nanowire and measured resistance changes 20 times larger than for a normal ferromagnet such as Cobalt.