January 19, 2019 – A group of Russian, Japanese and Spanish scientists tested the magnetic properties of polyanionic compounds through sodium iron phosphate (NaFePO4), an accessible, environmentally friendly and affordable substance. The scientists have published the results of their research in the British scientific journal Physical Chemistry Chemical Physics.

According to the results of the computer simulation conducted by the international research team at the International Center for the Nanoarchitectonics of Materials at the National Institute of Materials Science (Japan), it has been established that sodium iron phosphate (NaFePO4) exhibits a magnetoelectric effect when exposed to electric or magnetic fields: either the magnetization by an electric field or electric polarization by application of a magnetic field takes place.

‘This means that one can control the magnetic properties by applying the electric voltage to the sample, or vice versa, one can control the electric polarization by changing the magnetic properties. In other words, there is an opportunity for intermutual control of these properties,‘ Igor Solovyev, the author of the theoretical basis of the study, Doctor of Physical and Mathematical Sciences, UrFU scientist, explains.

For the first time, researchers were able to conduct an in-detail study of the the magnetic properties of sodium iron phosphate, which was previously considered only in relation to storage batteries.

‘Now, if we switch from the field of fundamental science into practical use, we know that sodium iron phosphate is a multifunctional compound that can be used in the production of not only batteries, but also chips and memory elements of mobile devices, where the magnetoelectric properties play a very important role,’ Sergey Nikolaev, a co-author, Candidate of Physical and Mathematical Sciences, Igor Solovyov’s colleague at Ural Federal University, said.

In other words, the multifunctionality of such compounds as sodium iron phosphate, and the diverse possibilities of their use, eliminates the need for other substances and makes the production of electronic devices simpler and cheaper.

The effect of chemical pressure on the magnetic properties of polyanionic compounds was studied as well by replacing sodium ions with lithium.

'Sodium iron phosphate has a porous structure and is convenient for such manipulations: it is easier to remove and add ions. We replaced big sodium with small lithium. Both the sample volume and its magnetic properties have changed, since they depend on the distance between the atoms,' Igor Soloviev describes.

Such studies, the scientist notes, are very important from the point of view of a theoretical study of the possibilities of increasing the temperature of magnetic ordering (in the long term – up to the room temperature), which is also crucial for the practical use of these phosphates’ magnetic properties.

Polyanionic compounds are high-molecular substances, polymers (cellulose, starch, rubber) with molecular weight of ten thousands to several million atomic mass units and with a large number of negatively charged groups of atoms. Such compounds are widely used: for instance, in rechargeable batteries as cathodes — negative electrodes connected to the negative contact of the current source (this is what is indicated by “-” on batteries).

Polyanionic compounds have unique electrochemical properties: ions of light elements (as a rule, alkali metals: lithium or sodium) are easily incorporated into their crystal lattice, filling unoccupied cavities there, and then leaving them, thus becoming free carriers of electric charge. Due to this feature, polyanionic compounds are suitable for the production of high-performance charging devices (like storage batteries), designed, for example, for mobile devices. In addition, polyanionic compounds are widely used in laboratory practice.

Many polyanionic compounds have exceptional magnetic properties. Thus, through an analogy with other oxides of transition metals, one might assume that some three-dimensional polyanionic compounds under certain conditions can become multiferroic. These are materials that are capable of spontaneous, arbitrary magnetization and polarizability without an external electric or magnetic field. This property determines their use in piezoelectric systems, heat gauges, sensors. In addition, some three-dimensional polyanionic compounds might induce magnetoelectricity: electric dipoles produced by an external magnetic field (dipoles are systems of two electric charges equal in magnitude and of opposite signs (positive and negative), which are at some distance from each other). However, these magnetic features of polyanionic compounds are understudied.

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