Researchers from Helmholtz-Zentrum Berlin demonstrated the possibility to locally switch on superferromagnetism in a wedge-shaped polycrystalline thin film of iron
The ability of electric field to control magnetism can aid in creating alternative magnetic and spintronic devices that offer high-end features, while consuming low power. There are several reported magnetoelectric effects, of which the ability to switch on and off long-range ferromagnetic arrays at ambient temperature, is of high importance. This feature in particular can be used to develop enhanced magnetoelectric data storage devices. Now, a team of researchers from Helmholtz-Zentrum Berlin (HZB), University of Paris-Sud, University of Paris-Saclay, Institute of Material Science of Barcelona, and University of Barcelona used a small electric field instead of magnetic fields to induce magnetic order on a small region of samples. The samples contain a wedge-shaped polycrystalline iron thin film that is deposited on top of a BaTiO3 substrate.
BaTiO3 has ferroelectric and ferroelastic properties and its lattice can be disturbed by an electric field. The electric field can also induce mechanical strain in the lattice. The team used electron microscopy for analysis and found that the iron film is made of grains that measure 2.5 nanometers (nm) in diameter, with a thickness of less than 0.5 nm. These nano-dimensions of the film allow magnetic moments of the iron nanograins to be disturbed. This lattice therefore, is induced in a state of superparamagnetism.
The team induced the nanograins with a small electric field to analyze its magnetic order and found that the electrical field was responsible for a strain on BaTiO3. This pressure was later passed to the iron nanograins. Moreover, the regions under superparamagnetic samples switched to a new state, where magnetic moments of the iron grains are all aligned in a uniform direction. This alignment known as superferromagnetism and can be used to design new composite materials. These materials can be used to create spin-based storage that consume low power. Moreover, logic architectures that work at room temperatures can also be achieved. The research was published in the journal Physical Review Materials on February 8, 2019.