According to the press service of the Russian Science Foundation, Krasnoyarsk scientists have shown the efficiency of the synthesis of nickel oxide nanoparticles in the oxygen plasma in a low-pressure arc reactor. This method of production will allow one to control the magnetic properties of nanoparticles, which make them suitable for use in computer memory devices and signal recording. The results of the study, supported by a grant from the Russian Science Foundation (RSF), are published in the journal Physica E: Low-Dimensional Systems and Nanostructures. In subsequent studies, also supported by a grant from the Russian Science Foundation and published in the IEEE Transactions on Dielectrics and Electrical Insulation, the scientists determined how the properties of nickel oxide nanoparticles depend on the conditions for this synthesis method.

Due to their size, nanoparticles have a number of unique electrophysical, chemical and optical characteristics. Of the greatest interest are magnetic nanoparticles with antiferromagnetic ordering. Electrons play a role of small magnets, and in such nanoparticles, the magnetic moments of the neighboring electrons are oriented antiparallel, so the total magnetization of the body is close to zero. The opposite situation is observed in ferromagnets, where the magnetic moments of the electrons are parallel and add up to the total magnetization of the body. Antiferromagnetic nanoparticles can be used as magnetic memory devices and to record audio and video signals such as magnetic tapes and hard disks. Devices based on these nanoparticles consume less energy and can be very small in size. Typically, memory devices need electricity to operate, but antiferromagnets do not need it to perform write operations. In addition, they are protected from erasure of information under the influence of an external magnetic field. The most popular are antiferromagnets based on transition metal oxides: nickel, copper and manganese. To obtain them, various physicochemical methods were used, one of which, plasma chemical, is distinguished by high productivity and allows one to control the size of nanoparticles, their structure and composition.

Russian scientists have shown for the first time that the production of nanoparticles in the oxygen plasma of a low-pressure arc discharge is an effective tool for the synthesis of nickel oxide (NiO) nanocrystalline particles. The synthesis takes place inside a reactor filled with gas (argon). The nickel cathode is heated to such an extent that it emits electrons and ionizes the gas inside the reactor. This gas forms a plasma which fills the entire volume. Then, oxygen is supplied to the chamber, creating a shell around the cathode, where the synthesis of NiO nanoparticles is carried out through the energy of plasma.

“The development of the method for synthesizing nanoparticles in the plasma of a low-pressure arc discharge will allow increasing the variety of nanoparticles to be obtained by this method for various purposes. In particular, nickel oxide is a suitable magnetic material for recording devices, since it can provide their miniaturization and increase the recording density, - says Anatoly Ushakov, Doctor of Technical Sciences, researcher at the Federal Research Center "Krasnoyarsk Science Center of SB RAS" and Siberian Federal University ... - Nickel oxide nanoparticles exhibit complex magnetic behavior depending on the magnetic field strength and temperature during synthesis. All the results obtained indicate that the nanoparticles have a noticeable magnetic response, and therefore can be used in recording devices. "

In subsequent studies, the scientists examined the structural features of the NiO nanoparticles obtained by the above method. Despite the fact that the electrical properties of this metal oxide are well studied, until now there have been no well-established ideas concerning the movement and location of charge carriers in nanoparticles. This is due to the fact that the properties of such materials strongly depend on the conditions of their preparation. Scientists showed that the characteristics of the NiO nanopowder synthesized in the plasma of a low-pressure arc discharge are determined mainly by the processes occurring near the cathode and depend on the rate of gas ionization. The synthesized samples were distinguished by the internal structure and high values of the dielectric constant in the low frequency range of electromagnetic waves. Such materials can be used as sensors, fuel cells and electrolyzers.