MOSCOW, February 16. /TASS/. Scientists from Moscow State University, Immanuel Kant Baltic Federal University (BFU, Kaliningrad) and the Institute of Natural Sciences and Mathematics of Ural Federal University (Yekaterinburg) have explained the mechanism of operation of a new multiferroic, which can be used in medicine and flexible electronics. They proved that elastic particle displacement plays an important role in magnetoelectric conversion, the BFU press service reported Wednesday.

Multiferroics are substances with both ferromagnetic (magnetization in the absence of an external magnetic field) and ferroelectric (occurrence of polarization in the absence of an external electric field) properties. Thus, they exhibit the effects associated with the interaction of electric and magnetic subsystems: magnetization induced by the electric field, change in the dielectric constant under the action of the magnetic field, switching of polarization by the magnetic field and magnetization by the electric field. Multiferroics are widely used in the modern world as detectors, frequency filters, energy converters. One of the advantages of modern multiferroics is their multifunctionality, meaning one element based on the multiferroic can "read" the changed information (work as a sensor), convert this information into a detectable signal (work as a converter), and, possibly in the future, accumulate energy for its further work.

The new polymer-based multiferroic is flexible and in some cases biocompatible, resistant to corrosive influences, and works even in a vacuum, all made possible by the use of polymers. It can be used in the flexible electronics fields, where, for example, the conversion or absorption of mechanical vibrations, electromagnetic energy is required. And due to the biocompatibility of the polymer, the magnetoelectric conversion can also be used for biomedical applications - wherever mechanical microactions, sensory characteristics, signal conversion, and autonomous operation are required.

The modeling and the experiment conducted in the course of the Russian scientist’s work show unique results for a new "smart" material - a multiferroic, consisting of a soft polymer with ferromagnetic and ferroelectric particles arranged inside.

"A model of multiferroic coupling of ferromagnetic and ferroelectric particles through elastic polymers was developed. Within the model, the ferromagnetic particles interact with each other as well as with the external magnetic field, while the ferroelectric particles also interact with each other and with the external electric field. All particles are connected by elastic virtual springs, including particles of different types. Simultaneously, numerical measurements were made of their electrical (magnetic) properties, including the external field (magnetic or electric). Change of magnetic (electric) properties under the influence of electric (magnetic) field means magneto-electric transformation. <...> An experiment was also carried out on a sample of elastomer <...>. The magnetic properties of the sample were measured in the absence and in the presence of an external electric field, and a comparison of the results between them showed their change, that is, the magnetoelectric effect," the press service quotes the words of Lyudmila Makarova, a researcher from the REC Smart Materials and Biomedical Applications at Immanuel Kant Baltic Federal University.

An unconventional magnetoelectric transformation mechanism

The work proved that purely elastic particle displacement plays a significant role in the magnetoelectric conversion, namely, in the conversion of electric field energy into magnetic and magnetic field energy into electric field energy. It differs significantly from currently known mechanisms in other types of multiferroics.

"The new multiferroic does not exhibit the classical conversion that usually occurs through magnetostriction (change in the size of the ferromagnetic) and the piezo effect. In our work, the magnetic particles in the sample shift under the action of the magnetic field, deforming the polymer medium, which leads to a change in the arrangement of the ferroelectric particles and, as a result, a change in the total electric polarization of the sample. This effect also works in the opposite direction: the electric field shifts the ferroelectric particles, forcing ferromagnetic particles through the elastic polymer and changing the total magnetic properties of the sample," explained the press service.

The key aspect is the softness of the polymer matrix. This means that even in the absence of a piezo matrix, in which electrical stresses would arise when mechanical deformations occur, a magnetoelectric effect is possible in materials based on a soft polymer.