New magnetoelectric multiferroic has room-temperature properties frozen in

A new material developed by researchers at the Paul Scherrer Institut (PSI) in Switzerland could become the basis for future data storage devices with substantially lower energy demands than present-day hard drives. The material is from a class known as magnetoelectric multiferroics, whose distinguishing characteristic is that their magnetic and electrical properties are coupled to each other.

Thanks to this coupling, it should be possible to write magnetic bits by means of energy-efficient electric fields, allowing this class of materials to serve as the basis for computer memories in the future. The advantage of this newly-developed multiferroic material is that it can exhibit the necessary magnetic properties even at room temperature, and not only – as with most magnetoelectric multiferroics to date – when cooled to very low temperatures (around -200°C). The PSI researchers report their new results in a paper in Nature Communications.

In magnetoelectric multiferroic materials, the magnetic and electrical properties are coupled to each other, allowing the magnetic properties to be controlled through the application of an electric field, which can be generated more easily and efficiently than magnetic fields. "When an electric field is applied to magnetoelectric multiferroics, it has an effect on the material's electrical properties," explains Marisa Medarde, lead author of the paper. "Through the magnetoelectric coupling, you then get a change in the magnetic properties for free."

Present-day computer hard drives store data in the form of magnetic bits that are written through the application of a magnetic field. In contrast, storage media based on multiferroics would have several advantages. Magnetic storage could be accomplished through the application of an electric field, which would require significantly less energy, and devices would produce less waste heat and thus would also have lower demands for cooling, reducing the use of fans and air conditioning. Given that cloud computing consumes many trillions of kilowatt-hours of power annually, savings in this area are of great importance.

The researchers came up with their new material by tailoring both the chemical composition and the exact production process. They ultimately found that a material with the chemical formula YBaCuFeO₅ becomes an effective magnetoelectric multiferroic if heated to a high temperature and then subjected to extremely fast cooling. "At high temperatures, the atoms arrange themselves in such a way as to be useful for our purposes," Medarde explains. "The rapid cooling essentially freezes this arrangement in place."

The underlying method of rapid cooling – also known as quenching – is familiar from the manufacture of especially hard metals and has been used for centuries, for example in tempering steel swords. The PSI researchers, however, applied much more extreme temperatures. They first heated the material to 1000°C, and then cooled it abruptly and rapidly to -200°C. After the material is removed from the cooling bath, it retains its special magnetic characteristics up to and somewhat above room temperature.

The synthesis and property optimization procedures were developed at PSI, where the materials were also produced and subsequently analyzed at two large-scale research facilities: the Swiss Spallation Neutron Source (SINQ) and the Swiss Light Source (SLS). "Our new material does not contain expensive ingredients," Medarde says. "And the production method – now that we have worked out the details – is easy to put into practice."

The new material owes its properties to the existence of so-called magnetic spirals at the atomic level; these tiny spirals are responsible for the coupling of magnetism and ferroelectricity. In most materials, magnetic spirals disappear when the material gets warmer than around -200°C. The PSI researchers see their main accomplishment as having created a material in which magnetic spirals are stable at room temperature. "Even at 30°C, our magnetic spirals were still present," says Medarde.

The material YBaCuFeO₅ is not completely new; it was actually synthesized for the first time in 1988. But the PSI researchers' special fabrication process precisely arranges the iron and copper atoms in such a way that the material acquires completely new properties. YBaCuFeO₅ is closely related to yttrium barium copper oxide (YBa₂Cu₃O_6+x), a group of superconductors discovered in 1987 that remain superconducting up to relatively high temperatures.

This story is adapted from material from the Paul Scherrer Institut, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.