CC BY
18
Chelyabinsk Physical and Mathematical Journal. 2021. Vol. 6, iss. 2. P. 255-263.
DOI: 10.47475/2500-0101-2021-16211
INFLUENCE OF HIGH PRESSURE TORSION ON MAGNETIC PROPERTIES Fe5oNi5o AND Fe49Ni49Al2 ALLOYS
M.N. Ulyanov1'2'", M.Yu. Bogush1, M.A. Gavrilova1, S.V. Taskaev1'3, Z. Hu4, D.V. Gunderov5'6, D.A. Zherebtsov3, E.P. Ulyanova3
1 Chelyabinsk State University, Chelyabinsk, Russia
2Immanuel Kant Baltic Federal University, Kaliningrad, Russia
3South Ural State University (National Research University), Chelyabinsk, Russia
4 University of Science and Technology Beijing, Beijing, P. R. China
5 Ufa State Aviation Technical University, Ufa, Russia
6Institute of Molecule and Crystal Physics RAS, Ufa, Russia " max-39@yandex.ru
We report on magnetic properties of FesoNiso and Fe49Ni49Al2 alloys after severe plastic deformation (SPD) by high pressure torsion (HPT) technique. SPD considerably changes the magnetization behavior. The main magnetic characteristics of bulk and HPT materials were determined. Low temperature annealing was used to form the L10 structure. Low temperature annealing at T = 300° C for t = 1300 hours of plastically deformed Fe49Ni49Al2 alloy leads to an increase in saturation magnetization MS by up to about 6%. However, it is premature to talk about the formation of even a small amount of phase L10. More research is required.
Keywords: Hard and soft magnetic materials, high pressure torsion, severe plastic deformation, rare-earth free metals, permanent magnet, low temperature annealing, tetrataenite.
Introduction
The China is a practically complete monopolist in the market of rare-earth elements. There are no alternatives to China in the supply of rare- earth elements. Growing in recent years, domestic demand for rare-earth elements in China has led to the restriction of their supplies to the international market, so there is an urgent need to develop alternative free rare-earth permanent magnets [1-6]. High performance permanent magnets have become indispensable materials in many industries, ranging from data storage to small motors and clean energy devices. Thus, the reduction of the content of critical elements in the production of permanent magnets is an adequate response to the crisis of the supply of rare-earth metals and their oxides and will make it possible to avoid the monopolistic dominance of China in the market of rare-earth elements.
Along with rare-earth systems, some Fe-based alloys are some of the most promising candidates for rare-earth compounds for the production of permanent magnets. Thus, the FeNi alloy with the L10 phase is a natural free rare-earth elements permanent magnet. Mineral tetrataenite has a high magnetization and energy density of magnetocrystalline anisotropy at room temperature in the range of 1.0-1.3 MJ/m3 [7] and also large uniaxial magnetocrystalline anisotropy constant (Ku) of bulk L10-FeNi is
This work is supported by Russian Science Foundation project no. 19-72-00047, by 5 top 100 Russian Academic Excellence Project at the Immanuel Kant Baltic Federal University and by Act 211 of Government of the Russian Federation, contract 02.A03.21.0011.
as large as 1.3x107 erg/cc. [8; 9], which are comparable to the properties of the most modern permanent magnets such as Nd-Fe-B [10] and other L10-type alloys containing noble metals: CoPt [11], FePt [12], and FePd [13]. Phase is stable only at temperatures below 600 K, therefore diffusion of atoms is difficult, and for the formation of the Ll0 phase from the Al phase billions of years are needed [14; 15] without any external influences [16; 17], therefore an example of a magnetic material with the L10 phase is an iron or ironstone meteorite. The magnetic properties of tetrataenite are almost unexplored due to the difficulty of obtaining such a phase [18; 19].
Since the discovery of the hard magnetic phase in a meteorite, the search began in its receipt in laboratory conditions. Novadays there are several articles in the international press on attempts to synthesize the magnetic hard L10 phase. The presence of a magnetic hard phase was detected on FeNi samples which irradiated by intense neutron fluxes, expressed in an increase in the coercive force and a change in the saturation magnetization of the irradiated FeNi sample [20; 21]. The synthesis of the tetrataenite phase in thin films of the FeNi alloy was reported in [22-25] — in the work of K.B. Reuter [22] reported about using the method of irradiation with electrons with high energy, and in [23-25] reported about using the method of molecular epitaxy.
In addition to the experimental work, first-principle calculations were carried out using the electron density functional theory of phase formation processes in the FeNi system. For example, the results of modeling the spin structure, saturation magnetization, and others for the alloy with the composition Fe2-x-yNixMy (M = Al, P, S, Ti, V, Cr, Mn, Fe, Co) are given in [26]. Doping with different elements can stabilize the structure, increase the amount of L10 phase in the parent matrix of the FeNi alloy, and improve the magnetic properties. Some of these elements are included in the calculations purely from scientific curiosity, but most came from experimental work on this topic. For example, in [27; 28] it was suggested that sulfur has a positive effect on the formation of the L10 phase. The addition of phosphorus to calculate the possible properties of tetrataenite was due to the fact that meteorites may contain minor amounts of the phase (Fe, Ni)3P, which, in turn, may influence the formation of the L10 phase.
In a previous work [29; 30], we reported the results of research in promising rare-earth free Fe-Ni-Ti alloys. The aim of this work is to study the magnetic properties of Fe49Ni49Al2 alloy after severe plastic deformation (SPD) by high pressure torsion (HPT) technique. Low temperature annealing is planned to use for the formation of the L10 phase.
Sample preparation and measurements
The Fe50Ni50 and Fe4gNi49Al2 alloy were prepared by argon-arc melting using a non-consumable tungsten electrode from the initial chemical elements Fe, Ni and Al with a purity of 99.99 at.%. The synthesized samples were inverted and remelted several times to achieve the best homogenization.
Our ingots were sliced and cut to disc about of 10 mm diameter and 1 mm thickness for HPT processing. The samples were placed between two anvils and was rotated under the applied pressure of 6 GPa at room temperature. SPD using HPT method were described in detail [31]. The total number of turns of the strikers for sample was n = 5. The diameter of the strikers was 10 mm.
X-ray diffraction (XRD) pattern were collected at room temperature by Brucker D8 Advance diffractometer using the monochromatic Cu Ka radiation and treated by modified Rietveld algorithm [32]. The elemental analysis of the synthesized materials
were carried out using energy dispersive X-ray fluorescence spectroscopy (EDX). Magnetization curves were measured by a PPMS Quantum Design VersaLab at T = 50-350 K in magnetic fields up to 3 T. Low temperature annealing was carried out at T = 300°C for t = 1300 hours.
Result and discussion
The results X-ray diffraction analysis bulk and HPT of Fe49Ni49Al2 samples are shown in Fig. 1. Severe plastic deformation by HPT method leads to the refinement of the structure of the material, which is reflected in the broadening of reflections on diffraction profiles. As the analysis shown, all samples are similar in phase composition and mainly consist of fcc (>99 wt%) and bcc (<1 wt%) phases. The lattice parameter a is equal (3.599 ± 0.001) A for Feso№50 bulk sample, is equal (3.600±0.001) A for Fe49Ni49Al2 bulk sample, is equal (3.578±0.001) A for Fe49Ni49Al 2 HPT sample. As seen the lattice parameter a change insignificantly with the addition of aluminum for bulk samples and decrease after SPD.
Fig. 1. X-ray diffraction pattern of bulk and HPT Fe49Ni49Al2 samples
The results of magnetic field dependences of magnetization of Fe50Ni50 and Fe49Ni49Al2 bulk samples at T = 300 K are shown in Fig. 2. The saturation magnetization MS for Fe50Ni50 bulk samples is 154.6 Am2kg-1 which is comparable, for example, with saturation magnetization of Morasko Meteorite-based Fe51 Ni49 in as-quenched state (curve in Fig. 2 [33]). The coercive field is 67.6 Oe, and remanence is 18 Am2kg-1. The saturation magnetization decreased up to 10% with the addition of 2% Al and is to 147.8 Am2kg-1, coercive field is 66.2 Oe, and remanence is 5.3 Am2kg-1 for Fe49Ni49 Al2 bulk sample. Almost the same values of the coercive force are also expected due to the fact that we study solid solution of aluminum in an iron-nickel alloy that are similar in composition.
As reported in [33], magnetization of the sample reaches its saturation MS at about 2 T. We observed that magnetization of our Fe50Ni50 and Fe49Ni49Al2 samples reaches its MS at about 0.5 T. Also we observed that the samples after HPT technique reaches
its saturation in significantly lower external magnetic field of about 0.2 T (Fig. 2). This behavior of magnetization is due to the microstructure and different shape anisotropy of bulk and HPT samples.
Fig. 3. Magnetic field dependences of magnetization of Fe49№49 Al2 bulk and HPT samples at T = 350 K
13-1-2-3
Fig. 2. Magnetic field dependences of magnetization of Fe-Ni bulk samples at T = 300 K. An enlarged low-field region of the hysteresis loop is shown in the inset. The result of magnetic field dependence of Morasko Meteorite-based Fe51 Ni49 in as-quenched state is shown by a green curve [33]
As a result of plastic deformation, the samples of Fe50Ni50 and Fe49Ni49Al2 in the submicrocrystalline state were obtained with high concentration of defects and stressed state. As seen in Fig. 3, a decrease in saturation magnetization was found caused by an increase in the concentration of defects after plastic deformation. Value of MS is about 8% smaller (145.2 Am2kg-1 and 136.9 Am2kg-1 for Fe50Ni50 and Fe49Ni49Al2 alloys respectively) for HPT samples compared with the saturation magnetization of the bulk samples. Also a decrease in the coercive force of the plastically deformed material was found compared to the bulk samples. Decrease in the coercive force HC is more than an order of magnitude. This behavior is quite different from most magnetic materials. One of the explanations may be the formation of a superparamagnetic state in which the coercive force is zero. The superparamagnetic state is interesting in that the loss of magnetization is practically zero due to the absence of magnetic hysteresis. The qualitative isothermal dependence of the coercive force HC on the characteristic size of magnetic particles is shown in Fig. 4. One of the reasons for the increase in HC with a decrease in the particle size is the following: with a decrease in the coercive force, more possibilities (mechanisms) appear for spin rotation in the direction opposite to the original. Rotation can be additionally associated with a displacement of the domain boundaries in multidomain particles. As the particle size decreases, the number of domains decreases, and the role of interdomain boundaries in magnetization reversal processes becomes less noticeable. Therefore, the coercive force increases with decreasing d up to the critical particle size dcrit. However, the role of thermal fluctuations increases with a further decrease in the particle size on going over to single-domain particles. This explains the decrease in HC at d < dcrit [34].
According to [35], subsequent low-temperature annealing should accelerate the kinetics of phase formation and, possibly, lead to the appearance of nuclei of a stable chemically ordered tetrataenite phase. Our research (Fig. 5 and Fig. 6) shown that low-temperature annealing at T = 300 0C for t = 1300 hours of plastically deformed Fe50Ni50 and Fe49Ni49Al2 samples leads to an increase in saturation magnetization MS by up to
6% for different compositions. The value of magnetization also increases to 5% in an external magnetic field fi0H = 3 T.
Fig. 4. Qualitative dependence of the coercive force HC on the diameter particles [34]
—3—^-0"
Fig. 5. Magnetic field dependences of magnetization before and after low temperature annealing at T = 300° C for t = 1300 hours of Fe49Ni49 Al49 and Fe50Ni50 HPT samples at T = 350 K
160
en 15Q
E <
140
130
2%T ^---^^ [i0H= 3T
■Fe49Ni49AI2HPT
-Fe49Ni4gAI2 annealing
300 h 1300°C 5%
-Fe50Ni50HPT
-Fe5QNi50 annealing
300 h 1300°C
T, K
W
Fig. 6. Temperature dependences of magnetization before and after low temperature annealing at T = 300°C for t = 1300 hours of Fe49Ni49 Al49 and Fe50Ni50 HPT samples in magnetic field H = 3 T
Conclusion
Tetrataenite (L10-FeNi) is a promising candidate for use as a permanent magnet of rare-earth free elements because of its favorable properties such as high magnetic anisotropy and coercivity. Soft magnetic Fe49Ni49Al2 and Fe50Ni50 metals were deformed by high pressure torsion and annealed at T = 300° C for t = 1300 hours for to form the Ll0 structure. When searching for phase we also used X-ray diffraction, energy dispersive spectroscopy, vibration sample magnetometry. However, our research shown that it is premature to talk about the formation of even a small amount of phase L10. More research is required.
References
1. Kramer K. Concern grows over China's dominance of rare-earth metals. Physics Today, 2010, vol. 63, pp. 22-24.
2. Sugimoto S. Current status and recent topics of rare-earth permanent magnets. Journal of Physics D: Applied Physics, 2011, vol. 44, p. 064001.
3. SkomskiR., Shield J.E., SellmyerD.J. An elemental question. In book: Magnetics Technology International. UKIP Media & Events, Ltd., 2011. Pp. 26-29.
4. Coey J.M.D. Permanent magnets: plugging the gap. Scripta Materialia, 2012, vol. 67, pp. 524-529.
5. Kramer M.J., McCallum R.W., Anderson I.A., Constantinides S. Prospects for Non-Rare Earth Permanent Magnets for Traction Motors and Generators. JOM, 2012, vol. 64, pp. 752-763.
6. BalamuruganB. et al. Prospects for nanoparticle-based permanent magnets. Scripta Materialia, 2012, vol. 67, pp. 542-547.
7. Lewis L.H., Pinkerton F.E., Bordeaux N., MubarokA., Poirier E., GoldsteinJ.I., SkomskiR., BarmakK. De magnete et meteorite: cosmically motivated materials. IEEE Magnetics Letters, 2014, vol. 5, pp. 1-4.
8. Pauleve J., Chamberod A., Krebs K., Bourret A. Magnetization curves of Fe-Ni (5050) single crystals ordered by neutron irradiation with an applied magnetic field. Journal of Applied Physics, 1968, vol. 39, p. 989.
9. OhtsukiT., KotsugiM., OhkochiT., LeeS., HoritaZ., TakanashiK. Nanoscale characterization of FeNi alloys processed by high-pressure torsion using photoelectron emission microscope. Journal of Applied Physics, 2013, vol. 114, p. 143905.
10. BurkertT., Nordstrom L., Eriksson O., HeinonenO. Giant magnetic anisotropy in tetragonal FeCo alloys. Physical Review Letters, 2004, vol. 93, p. 027203.
11. Lin C.J., Gorman G.L. Evaporated CoPt alloy films with strong perpendicular magnetic anisotropy. Applied Physics Letters, 1992, vol. 61, p. 1600.
12. InoueK., ShimaH., FujitaA., IshidaK., OikawaK., Fukamichi K. Temperature dependence of magnetocrystalline anisotropy constants in the single variant state of L10-type FePt bulk single crystal. Applied Physics Letters, 2006, vol. 88, p. 102503.
13. ShimaH., OikawaK., FujitaA., FukamichiK., IshidaK., SakumaA. Lattice axial ratio and large uniaxial magnetocrystalline anisotropy in L1o-type FePd single crystals prepared under compressive stress. Physical Review B, 2004, vol. 70, p. 224408.
14. YangC.W., Williams D.B., Goldstein J.I. A revision of the Fe-Ni phase diagram at low temperatures (<400 °C). Journal of Phase Equilibria, 1996, vol. 17 (6), p. 522.
15. Mizuguchi M., Sekiya S., Takanashi K. Characterization of Cu buffer layers for growth of L10-FeNi thin films. Journal of Applied Physics, 2010, vol. 107, p. 09A716.
16. KojimaT., Mizuguchi M., Koganezawa T., Osaka K., KotsugiM., TakanashiK. Magnetic anisotropy and chemical order of artificially synthesizedL10-ordered FeNi films on Au-Cu-Ni buffer layers. Japanese Journal of Applied Physics, 2012, vol. 51, p. 010204.
17. Wasilewski P. Magnetic characterization of the new magnetic mineral tetrataenite and its contrast with isochemical taenite. Physics of the Earth and Planetary Interiors, 1998, vol. 52, pp. 150-158.
18. SkomskiR., Coey J.M.D. Permanent Magnetism. Bristol, Institute of Physics, 1999.
19. SkomskiR., ManchandaP., Kumar P., BalamuruganB., KashyapA., Sellmyer D.J. Predicting the future of permanent-magnet materials. IEEE Transactions on Magnetics, 2013, vol. 49 (7), pp. 3215-3220.
20. Neel L., Pauleve J., Pauthenet R., Laugier J., Dautreppe D. Magnetic properties of an Iron-Nickel single crystal ordered by neutron bombardment. Journal of Applied Physics, 1964, vol. 35, p. 873.
21. NeelL., Pauleve J., Dautreppe D., Laugier J. Une nouvelle transition ordre-desordre dans Fe-Ni (50-50). Comptes Rendus de l'Académie des Sciences, 1962, vol. 254, p. 965; Journal de Physique et Le Radium, 1962, vol. 23, pp. 841-843.
22. ReuterK.B., Williams D.B., Goldstein J.I. Ordering in the Fe-Ni system under electron irradiation. Metallurgical and Materials Transactions A, 1989, vol. 20, pp. 711718.
23. ShimaT., OkamuraM., MitaniS., TakanashiK. Structure and magnetic properties for L10-ordered FeNi films prepared by alternate monatomic layer deposition. Journal of Magnetism and Magnetic Materials, 2007, vol. 310, pp. 2219-2214.
24. KojimaT., Mizaguchi M., Takanashi K. Ll0-ordered FeNi film grown on Cu-Ni binary buffer layer. Journal of Physics: Conference Series, 2011, vol. 266, p. 012119.
25. MizuguchiM., KojimaT., KotsugiM., KoganezawaT., OsakaK., TakanashiK. Artificial fabrication and order parameter estimation of L10-ordered FeNi thin film grown on a AuNi buffer layer. Journal of the Magnetics Society of Japan, 2011, vol. 35, pp. 370373.
26. ManchandaP., SkomskiR., BordeauxN., LewisL.H., KashyapA. Transition-metal and metalloid substitutions in L10-ordered FeNi. Journal of Applied Physics, 2014, vol. 115, p. 17A170.
27. MaL., Williams D.B., Goldstein J.I. Determination of the Fe-rich portion of the Fe-Ni-S phase diagram. Journal of Phase Equilibria, 1998, vol. 19, p. 299.
28. Kabanova I.G., Sagaradze V.V., KataevaN.V. Formation of an L10 superstructure in austenite upon the a ^ y transformation in the invar alloy Fe-32% Ni. Physics of Metals and Metallography, 2011, vol. 112, p. 267.
29. TaskaevS.V., UlyanovM.N., Gunderov D.V., BogushM.Yu. Magnetic properties of ternary Fe-Ni-Ti alloys after severe plastic deformation. IEEE Magnetics Letters, 2020, vol. 11, p. 7502805.
30. UlyanovM.N., TaskaevS.V., Shevyrtalov S.N., Medvedskaya P., Gunderov D.V. Structural properties of Fe4gNi4gAl2 alloy deformed by high pressure torsion. AIP Advances, 2021, vol. 11 (2), p. 025311.
31. SakaiG., HoritaZ., LangdonT.G. Grain refinement and superplasticity in an aluminum alloy processed by high-pressure torsion. Materials Science and Engineering: A, 2005, vol. 393, pp. 344-351.
32. Shelekhov E.V., Sviridova T.A. Programs for X-ray analysis of polycrystals. Metal Science and Heat Treatment, 2000, vol. 42, pp. 309-313.
33. Kolodziej M., SniadeckiZ., MusialaA., PierunekN., Ivanisenko Yu., MuszynskiA., IdzikowskiB. Structural transformations and magnetic properties of plastically deformed FeNi-based alloys synthesized from meteoritic matter. Journal of Magnetism and Magnetic Materials, 2020, vol. 502, p. 166577.
34. Mehrmohammadi M., YoonK.Y., QuM., Johnston K.P., Emelianov S.Y. Enhanced pulsed magneto-motive ultrasound imaging using superparamagnetic nanoclusters. Nanotechnology, 2010, vol. 22, p. 045502.
35. GotoS., KuraH., WatanabeE., HayashiY., YanagiharaH., ShimadaY., MizuguchiM., TakanashiK., KitaE. Synthesis of single-phase L10-FeNi magnet powder by nitrogen insertion and topotactic extraction. Scientific Reports, 2017, vol. 7, p. 13216.
Article received 04.03.2021.
Corrections received 30.04.2021.
Челябинский физико-математический журнал. 2021. Т. 6, вып. 2. С. 255-263.
УДК 621.318 DOI: 10.47475/2500-0101-2021-16211
ВЛИЯНИЕ КРУЧЕНИЯ ПОД ВЫСОКИМ ДАВЛЕНИЕМ НА МАГНИТНЫЕ СВОЙСТВА Fe5oNi5o И Fe49Ni49Al2 СПЛАВОВ
М. Н. Ульянов1'2'", М. Ю. Богуш1, М. А. Гаврилова1, С. В. Таскаев1'3, Д. Ху4, Д. В. Гундеров5'6, Д. А. Жеребцов3, Е. П. Ульянова3
1 Челябинский государственный университет, Челябинск, Россия
2 Балтийский федеральный университет им. И. Канта, Калининград, Россия 3Южно-Уральский государственный университет
(национальный исследовательский университет), Челябинск, Россия
4 Пекинский университет науки и технологий, Пекин, Китай
5 Уфимский государственный авиационный технический университет, Уфа, Россия 6Институт физики молекул и кристаллов УФИЦ РАН, Уфа, Россия
" max-39@yandex.ru
Исследованы магнитные свойства сплавов Fe5oNi5o и Fe4gNi4gAl2, подвергнутых интенсивной пластической деформации (ИПД) методом кручения под высоким давлением. ИПД значительно изменяет поведение намагничивания. Определены основные магнитные характеристики литых и пластически деформированных материалов. Для формирования структуры L1o использовался низкотемпературный отжиг. Низкотемпературный отжиг при температуре T = 300 ° C в течение t = 1300 часов пластически деформированного сплава Fe4gNi4gAl2 приводит к увеличению намагниченности насыщения Ms примерно до 6 %. Однако говорить об образовании даже небольшого количества фазы L1o преждевременно. Требуются дополнительные исследования.
Ключевые слова: мягкие и жёсткие магнитные материалы, кручение под высоким давлением, интенсивная пластическая деформация, безредкоземельные металлы, постоянный магнит, низкотемпературный отжиг, тетратенит.
Поступила в редакцию 04.03.2021. После переработки 30.04.2021.
Сведения об авторах
Ульянов Максим Николаевич, кандидат физико-математических наук, старший научный сотрудник кафедры общей и прикладной физики, Челябинский государственный университет, Челябинск, Россия; научный сотрудник лаборатории исследования магнитных явлений на рентгеновских источниках нового поколения МНИЦ «Когерентная рентгеновская оптика для установок «Мегасайенс», Балтийский федеральный университет им. И. Канта, Калининград, Россия; e-mail: max-39@yandex.ru.
Богуш Михаил Юрьевич, аспирант, лаборант-исследователь кафедры общей и прикладной физики, физический факультет, Челябинский государственный университет, Челябинск, Россия; e-mail: bmy74@yandex.ru.
Гаврилова Мария Алексеевна, студентка, лаборант-исследователь кафедры общей и прикладной физики, физический факультет, Челябинский государственный университет, Челябинск, Россия; e-mail: mariya-fks@mail.ru.
Работа поддержана Российским научным фондом, проект № 19-72-00047, проектом «5-100» повышения конкурентоспособности ведущих российских университетов в Балтийском федеральном университете им. И. Канта и Постановлением № 211 Правительства Российской Федерации, договор 02.A03.21.0011.
Таскаев Сергей Валерьевич, доктор физико-математических наук, доцент, профессор кафедры физики конденсированного состояния, физический факультет, Челябинский государственный университет; научный сотрудник управления инновационной деятельности, Южно-Уральский государственный университет (национальный исследовательский университет), Челябинск, Россия; e-mail: tsv@csu.ru.
Джанг Ху, профессор школы материаловедения и инженерии, Университет науки и технологий Пекина, Пекин, Китай; e-mail: zhanghu@ustb.edu.cn.
Гундеров Дмитрий Валерьевич, доктор физико-математических наук, ведущий научный сотрудник, заведующий лабораторией физики наноструктурных материалов, Институт физики молекул и кристаллов УФИЦ РАН; ведущий научный сотрудник, руководитель группы «Наноструктурные метастабильные сплавы и материалы с эффектом памяти формы», Институт физики перспективных материалов, Уфимский государственный авиационный технический университет, Уфа, Россия; e-mail: dimagun@mail.ru. Жеребцов Дмитрий Анатольевич, доктор химических наук, доцент, старший научный сотрудник управления инновационной деятельности, Южно-Уральский государственный университет (национальный исследовательский университет), Челябинск, Россия; email: zherebtcovda@susu.ru.
Ульянова Евгения Павловна, кандидат филологических наук, доцент кафедры РКИ, Южно-Уральский государственный университет (национальный исследовательский университет), Челябинск, Россия; e-mail: marzhenya@yandex.ru.
