Unique palladium-iron films grown at KFU
The research was carried out at the Laboratory Heterostructures for Post-Silicon Electronics of the Institute of Physics by Lenar Tagirov, Chief Research Associate, Academician of the Academy of Sciences of the Republic of Tatarstan, Roman Yusupov, Lead Research Associate, Head of the Department of Quantum Electronics and Radio Spectroscopy, senior research associates of the laboratory Amir Gumarov and Igor Yanilkin, as well as Lead Research Associate of the Laboratory of Quantum Simulators Airat Kiyamov and Research Associate of the Laboratory of Multifunctional Nanostructures and Photonics Crystals for Solving Fundamental Problems of Biomedicine and Materials Science" Bulat Gabbasov. Igor Golovchansky, Lead Research Associate of the Laboratory of Topological Quantum Phenomena in Superconducting Systems of the Center for Advanced Methods of Mesophysics and Nanotechnologies of the Moscow Institute of Physics and Technology, took part in the work.
The research work was carried out as part of the Study of spin-wave resonance in epitaxial films of PdFe and PdCo alloys with a given magnetic impurity concentration profile project supported by the Russian Science Foundation.
"Spin waves or magnons are intrinsic excitations of magnetic moments propagating in a magnetic material, such as a ferromagnetic, antiferromagnetic or ferrimagnetic, via exchange or magnetostatic interactions. Spin waves are promising for information transfer and processing in magnonics, a new and burgeoning field of spin-wave electronics. Scientists have now learned how to excite, transmit and read magnons, but the spin wave spectrum of known magnetic materials is quite well defined, which creates problems of interfacing different magnetic materials in magnonics processors. However, advances in technologies to create thin films with man-made magnetic properties offer great potential for controlling the spin wave spectrum. New knowledge about how the magnetic structure of the film affects the excitation, propagation and attenuation of spin waves will contribute to the development of magnonics in the direction of information transmission and processing," comments project lead Amir Gumarov.
According to theoretical calculations, films with inhomogeneous magnetic properties allow to control both standing and propagating spin waves. To date, there are very few experimental works devoted to the synthesis of magnetic materials with a predetermined profile of the distribution of magnetic properties ('gradient' magnetic materials). Among the methods of obtaining gradient materials we can mention the method of chemical deposition, liquid-phase epitaxy, magnetron sputtering, and the method of ion implantation. The technology of molecular beam epitaxy for the purpose of creating gradient magnetic materials was first used by KFU scientists.
"The palladium-iron alloy turned out to be ideal for creating a gradient magnetic material based on it. First, an important advantage of this alloy is the possibility of tuning its magnetic parameters: saturation magnetization, coercive field, exchange splitting energy of the conduction zone and magnetic anisotropy by changing the concentration of iron. Secondly, this noble metal-based alloy does not oxidize over time and does not change its magnetic properties for decades. Finally, we can set the profile of iron concentration distribution in the palladium matrix in a controlled way, i.e. make it, for example, linear, parabolic, sinusoidal, or more complex. The latter allowed us to observe the manifestation of magnon modes localized in the potential well of an artificially set magnetic profile. We can say that we managed to control its spin-wave resonances by profiling the magnetic properties of the film. Each spin-wave mode is a string vibrating with its own frequency. Control of spin-wave resonances can be compared to tuning the strings of a musical instrument," explains Igor Yanilkin.
To obtain the desired alloys the researchers used two evaporator cells that contained the starting materials – palladium and iron. In the process of film growth, the temperature of the cell with palladium remained constant, while the temperature of the cell with iron was changed according to a pre-programmed protocol for changing the rate of heating/cooling of the cell in time, which allowed to grow films with heterogeneous distribution of iron in the palladium matrix.
"This is not our first experience in obtaining a heterogeneous distribution profile of iron magnetic impurity in a palladium matrix. Previously, we used ion implantation of iron atoms into pre-grown single-crystal palladium films. However, this method, unlike molecular beam epitaxy, did not allow us to precisely control the profile of iron concentration distribution over the film thickness, which made it difficult to control the spectrum of intrinsic magnon modes," says Lenar Tagirov.
The main purpose of synthesizing gradient films based on palladium-iron alloy was to study the possibility of controlling the spectrum of standing spin-wave resonances. For this purpose, the scientists investigated the excitation of spin waves in them by ferromagnetic resonance in different geometries and measurement temperatures. According to Roman Yusupov, the main experimental result was the observation of a resonance absorption pattern corresponding to a predetermined ferromagnetic profile of the films. He also added that the measured spin-wave resonance spectra are well described within the existing theory.
"Our samples are low-temperature ferromagnetics, but we have shown that it is possible to shift the gradient interval of the iron concentration gradient in palladium so that spin waves are also observed at room temperature, which is important for practical applications in magnonics that do not require cooling of components," the scientist notes.
The results saw light in Journal of Vacuum Science & Technology A.
More information:
Molecular beam epitaxy of Pd-Fe graded alloy films for standing spin waves control
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Provided by Kazan Federal University