Magnetic switch gets closer to application

XMCD-PEEM asymmetry images of FeRh obtained at the Fe L3-edge at 385 K. The presence of blue/red domains at 0 Volts (left panel) are related to the presence of ferromagnetic domains showing thus that the FeRh film is ferromagnetic. After applying 50 V (right panel) the red/blue ferromagnetic domains disappear pointing out that the FeRh film is now antiferromagnetic.

XMCD-PEEM asymmetry images of FeRh obtained at the Fe L3-edge at 385 K. The presence of blue/red domains at 0 Volts (left panel) are related to the presence of ferromagnetic domains showing thus that the FeRh film is ferromagnetic. After applying 50 V (right panel) the red/blue ferromagnetic domains disappear pointing out that the FeRh film is now antiferromagnetic. © HZB

Scientists from Paris, Newcastle and Helmholtz-Zentrum Berlin have been able to switch on and off robust ferromagnetism close to room temperature by using low electric fields. Their results are inspiring for future applications in low-power spintronics, for instance in fast, efficient and nonvolatile data storage technologies.

The sample consisted of a ferroelectric BaTiO3 substrate covered with a thin film of magnetic FeRh.  Experiments at BESSY II combined with other measurement methods demonstrated how the magnetic order of the sample changes dramatically, when a moderate external electric field is applied: The electric field induces strain in the crystal structure of the ferroelectric substrate, which is transferred to the thin FeRh-film and switches its magnetic ordering from ferromagnetic (large magnetization) to antiferromagnetic (zero magnetization). The effect is ten times larger than previously observed in other magnetic structures and especially promising since it is found close to room temperature. The results have been published online on 26 January in Nature Materials, DOI: 10.1038/NMAT3870.

The ability to turn on and off robust ferromagnetism at room temperature and low electric fields has remained elusive until now. Nevertheless, such magnetic switches would be extremely useful for spintronic devices and future data storage technologies.

Now a materials system has been grown by scientists at Unité Mixte de Physique CNRS/Thales and Université Paris Sud which has interesting properties. As measurements of Sergio Valencia, Akin Ünal and Florian Kronast from HZB demonstrated, their magnetization can be controlled by means of electric fields. The change achieved in the magnetization with moderate electric field is one magnitude higher than observed previously in any other materials:
The new structure consists of a ferroelectric BaTiO3 crystal substrate, covered with a thin film of magnetic FeRh. To obtain microscopic information about the magnetic order, the HZB team took high-resolution magnetic images at the spin-resolved photo-emission electron microscope at BESSY II at different voltages at a temperature of 385 K or 112 °Celsius. “We have found that in FeRh/BaTiO3 even a moderate electric field can produce a giant magnetization variation, arising from the electric-field-induced transformation of the FeRh from an ferromagnetic state to an antiferromagnetic state”, Valencia says.

The detailed analysis of the data in the light of first-principles calculations indicate that the phenomenon is mediated by both strain and field effects from the BaTiO3. The results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude. The possibility of toggling between magnetic states by means of an electric field and at very low power offers an attractive alternative to heat-assisted magnetic recording. This technology uses a laser pulse to heat a magnetic bit above a certain temperature at which the magnetic field generated by the write-head can reliably switch the magnetization direction. “On a broader perspective, our work emphasizes the relevance of hybrid perovskite/metal systems such as BaTiO3/FeRh for low-power spintronic architectures. In the future, it would be attractive to combine  FeRh with piezoelectric elements with giant responses. The effect could be further increased and tuned to a range of operating temperatures, including room temperature, by using Palladium-substituted FeRh”, Valencia points out.

arö


You might also be interested in

  • 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.
  • Catherine Dubourdieu receives ERC Advanced Grant
    News
    30.03.2023
    Catherine Dubourdieu receives ERC Advanced Grant
    Prof. Dr. Catherine Dubourdieu heads the Institute “Functional Oxides for Energy-Efficient Information Technology” at HZB and is Professor at the Physical and Theoretical Chemistry division at Freie Universität Berlin. The physicist and materials scientist specialises in nanometre-sized functional oxides and their applications in information technologies. She has now been awarded a prestigious ERC Advanced Grant for her research project “LUCIOLE”, which aims at combining ferroelectric polar textures with conventional silicon technologies.
  • Scientists Develop New Technique to Image Fluctuations in Materials
    Science Highlight
    18.01.2023
    Scientists Develop New Technique to Image Fluctuations in Materials
    A team of scientists, led by researchers from the Max Born Institute in Berlin and Helmholtz-Zentrum Berlin in Germany and from Brookhaven National Laboratory and the Massachusetts Institute of Technology in the United States has developed a revolutionary new method for capturing high-resolution images of fluctuations in materials at the nanoscale using powerful X-ray sources. The technique, which they call Coherent Correlation Imaging (CCI), allows for the creation of sharp, detailed movies without damaging the sample by excessive radiation. By using an algorithm to detect patterns in underexposed images, CCI opens paths to previously inaccessible information. The team demonstrated CCI on samples made of thin magnetic layers, and their results have been published in Nature.