UNN scientists jointly with other physicists develop the basis for alternative electronics
Together with colleagues from the Saratov State University, the Fryazino branch of the RAS Institute of Radio Engineering and Electronics and the RAS Institute for Physics of Microstructures, Lobachevsky University researchers have developed thin multilayer films that may become the basis for alternative electronics.
The project is aimed at designing a technology for obtaining and studying the properties of multilayer ferromagnet/heavy metal (FM/HM, where FM = Co, HM = Pt, Pd) thin-film structures with no clear boundaries. Currently, FM/HM films are considered as a promising material for manufacturing components for spintronics, as well as for information storage and processing devices. The useful functions of these materials are based on their unique magnetic properties, such as the presence of perpendicular magnetic anisotropy and strong spin-orbit interaction. Moreover, it is believed that the magnetic properties of the films are largely determined by the Dzyaloshinskii-Moriya surface interaction (DMI) arising at the layer boundary. It is the presence of DMI that explains the existence of skyrmions, nontrivial magnetic structures that possess (from the theoretical point of view) the property of topological stability. In practical terms, this makes them interesting for producing non-volatile memory elements.
"The peculiarity of our project is that the films are formed by electron-beam evaporation, unlike most other approaches that use the magnetron sputtering method. The advantage of electron-beam evaporation is the lower energy of particles being deposited compared to magnetron sputtering. This allows the electron-beam evaporation method to be used to form ferromagnetic films directly on the surface of semiconductor nanostructures, minimising the amount of defects introduced into the near-surface regions of the semiconductor. In this case, the nominal thickness of cobalt magnetic layers (1-3 Å) is extremely small (less than the lattice parameter), several times less than typical values used in magnetron sputtering. Therefore, it is possible to form polycrystalline alloys in the film, which are a combination of several crystalline phases. Such samples correspond to the class of multilayer structures with fuzzy boundaries," said Mikhail Dorokhin, leading researcher at the UNN Physics and Technology Research Institute.
To accomplish the research objectives, the technological and research equipment available at Lobachevsky University was used (including technological growth units, equipment for X-ray diffraction studies and X-ray phase analysis, X-ray photoelectron spectroscopy for chemical analysis, magnetic force microscopy for the study of micromagnetic structure, etc.). Advanced equipment of the Shared Use Centre "Physics and Technology of Micro- and Nanostructures" at the RAS Institute for Physics of Microstructures (transmission electron microscopy, scanning electron microscopy, secondary ion mass spectrometry) was also used in the project.
As a result of the project, the theory of Dzyaloshinski-Moriya interaction in FM/HM films in the absence of a direct boundary between ferromagnetic and heavy metal layers was developed, the processes of skyrmion nucleation and the possibilities of controlling skyrmions were investigated, and the effect of chiral magnetic structures on the transport properties of films was studied.
The effects of phase and chemical composition on the magnetic properties of ferromagnet/heavy metal films were studied, and technological modes were determined that allow controlling the most important magnetic characteristics of the films, which affect the Dzyaloshinskii-Moriya interaction energy. At the current stage of the project, the developed technologies are being tested in the process of producing laboratory samples of new generation electronics devices.
