CC BY
9Journal of Siberian Federal University. Engineering & Technologies 1 (2015 8) 48-56
УДК 539.213.536
The Clusters Self-Assembled Crystal
and Magnetic Structure During
the Martensite Transition in Fe86mn13c Alloy
Ludmila I. Kveglisa,e, Alexey V. Dzhesb, Micail N. Volochaev c, Alexander G. Cherkov d and Fedor M. Noskova*
aSiberian Federal University 79 Svobodny, Krasnoyarsk, 660041, Russia bEast Kazakhstan State Technical University 69 А.К. Protozanov, Ust-Kamenogorsk, 070004, The Republic of Kazakhstan cKirensky Institute of Physics 50/38 Akademgorodok, Krasnoyarsk, 660036, Russia
dNovosibirsk State University 2 Pirogov, Novosibirsk, 630090, Russia eEast Kazakhstan State University 55 Kazakhstan, Ust-Kamenogorsk, 070004, The Republic of Kazakhstan
Received 07.10.2014, received in revised form 21.10.2014, accepted 16.01.2015
In bulk and thin film state Fe86Mn13C alloy observed experimentally self-assembly of the crystal and magnetic structures on multiscale levels. Offered self-assembly cluster model of atomic structure based on the concept of a liquid-like state of the material in localized areas, formed in the waves of plastic deformation.
Keywords: Thin magneticfilms, Fe86Mn13C alloy, close packed structure clusters, magnetic structure, martensite transitions, density of electronic states, waves ofplastic deformation.
© Siberian Federal University. All rights reserved Corresponding author E-mail address: [email protected]
*
Кластерная самоорганизация
кристаллической и магнитной структур
в процессе мартенситного превращения в сплаве Fe86Mn1зC
Л.И. Квеглиса' д, А.В. Джесб, М.Н. Волочаевв, А.Г. Черковг, Ф.М. Носкова
а Сибирский федеральный университет Россия, 660041, Красноярск, Свободный, 79 бВосточно-Казахстанский государственный технический университет Республика Казахстан, 070004 Усть-Каменогорск, Протозанова А.К., 69 вИнститут физики им. Л.И. Киренского СО РАН Россия, 660036, Красноярск, Академгородок, 50, стр. 38 г Новосибирский государственный университет Россия, 630090, Новосибирск, ул. Пирогова, 2 дВосточно-Казахстанский государственный университет
Республика Казахстан, 070004 Усть-Каменогорск, Казахстанская, 55
В массивных и тонкопленочных образцах сплава Fe86Mn13C экспериментально наблюдается самоорганизация кристаллической и магнитной структур на разномасштабных уровнях. Предлагается кластерная модель атомной самоорганизации, основанная на концепции жидкоподобного состояния материала в локальных участках, образованных волнами пластической деформации.
Ключевые слова: тонкие магнитные пленки, сплав Fe86Mn13C, кластеры с плотноупакованной структурой, магнитная структура, мартенситные превращения, плотность электронных состояний, волны пластической деформации.
Introduction
The Fe86Mn13C alloy is widely used in engineering as a self-strengthening material under the influence of shock loading and it has shape memory effect. Fe-Mn films are investigated as materials for spintronics due to their unique properties [1]. First the most fundamental work devoted to the synergistic mechanism of deformation of a solid state under the influence of external loads is to work [2]. One of the first works devoted to the problem of self-assembly of magnetic domain structure was the work [3]. In thin film technology the pressure at the interface between the film and the substratecan be up to 7 Gpa due to differences in thermal expansion coefficients and nonlinear effects.
The results of studies on the structure, phase composition and magnetic structure of thin films of magnetic alloy Fe86Mn13C, obtained under different conditions are presented. The methods of transmission electron microscopy techniques including Lorentz microscopy were used.
In the alloy Fe86Mn13C previously discovered the thermoelectric effect [4]. The thermoelectromotive force and magnetoresistance in Fe86Mn13C alloy reverses its sign in a certain range of temperatures. Modulated structure - antiferromagnetic austenite and ferromagnetic deformation martensite formed
in conditions of plastic deformation of the alloy Fe86Mn13C. This particularity creates a unique electrical and magnetic properties of the alloy [4, 5]. In this regard, thin films Fe86Mn13C, having a modulated structure, can be used as a spintronic material [6].
The aim of this work is examination of the crystal and magnetic structure for the bulk, thining foil and thin film states of this alloy, subjected to plastic deformation leads to martensite transition.
Research methods
Fe86Mn13C films were obtained on glass and NaCl substrates by thermal vacuum evaporation at a pressure of 10-5 Torr using a VUP-4 installation. The thin-film samples then underwent cryomachining, i.e. repeated immersion in liquid nitrogen with intermediate endurance at room temperature for several minutes. Since thermal expansion coefficients of the film and the substrate differed several times from glass NaCl, MgO the film sample was tested under an effective loading of about 7 Gpa. The structure and magnetic contrast of the films were investigated using EM-200 and JEM-2100 transmission electron microscopy, including Lorentz electron microscopy and electron diffaction techniques. High resolution electron microscopy methods for investigation of atomic and magnetic structures in Fe86Mn13C thin films. The films were prepared at different substrate temperatures: room temperature (25 °C) and 200 °C, 300 °C and 400 °C. At each temperature of substrate the evaporation was carried out with different time: short time (~ 7.5 s) and long time (~ 30-40 s). Spin polarized density of electronic states for clusters FK12, FK14, FK16 simulated by the method of Slater theory of the scattered waves for comparing the energy of the optical transitions with energy obtained from the calculation of the spin-polarized electron density of states for FK12 and FK16. The optical properties were investigated on adsorption spectrometer Shimadzu UV 3600.
Experemental results and discussion
We explain features of thermoelectrisity and magnetoresistivity in terms of coexistence of heterogeneous crystalline and magnetic structures in the samples Fe86Mn13C alloy. At the Fig. 1 dark strings correspond to deformation martensite in initial austenite phase (light areas). Similar striped structure was observed on bulk samples in work [4] of the alloy in the period between the stripes was a few microns.
Fig. 2,a b, c, shows electron microscope image of a magnetic contrast from the alloy films Fe86Mn13C, obtained with the different substrate temperature. The magnetic structure in Fig. 2,a is bubble, magnetic structure at Fig. 2,b is predominantly "a stripe" character. The magnetic structure at Fig. 2,c is vortex.
Electron diffraction patterns Fig. 2,d indicate the presence of the bcc phase in addition to the quasicrystalline inclusions, which is typical for structures Frank-Kasper FK-12 + FK-16 [7].
Under such conditions, the deposition film structure appears Frank-Kasper type FK16. This structure was detected by electron diffraction pattern decoding.
At the Fig. 3 a,b the resultes of clusters modeling Frank-Kasper structures FK16 and FK12 are represented. Polyhedrons with 16 vertices and 12 vertices are connected by triangular faces.
We previously observed structure of the type FK12+FK16 for thinning foils alloy Fe86MnBC by X-ray diffraction method. Fig. 3,c shows this picture. We used for comparison, the X-ray diffraction pattern having a structure FK16+FK12. This picture represented at Fig. 3,d.
Fig. 1. High resolution electron microscopy image of micro structure Fe86Mn13C alloy after loading in liquid nitrogen each dark; regian is magnetic martensite phase: a - thinning foil; b - ehin film
Fig. 2. The Lorentz electron microscopy images of domain structures Fe86Mn13C films obtained at different temperatures of substrates: a - 200 °C; b - 300 °C; c - 400 °C; d - the picture of electrons diffraction for 400 °C
_i_i_
.JL
U
X <6
d
Fig. 3. The structures of Frank-Kasper FK 16 and FK12: a - the model of cluster FK 16; b - Frank-Kasper structures MgCur (FFK 16 + FK12); c - X-ray diffraction spectra from thtnning foil Fe86Mn13C alloy; d - X-ray diffraction spectra for the structure MgCu2, consist of clusters FK 16 and FK 12
r
Acc ording to works of V.E. Panin [8] nucleation phase and martensite deformation in alloys occurs at deformation defects. The author describes a deformable solid as a multilevel donlinear hierarchically ooganized system. Considered highly excited struetutal states, among which in a deformed crystal are allowed new structural condition. Changing the interatomic distance causes the occurrence of the bifurcation of the potential minima of the particles.
With increasing degree of plastic deformation, the translational invariance of the crystal decreases ppogeessivelp [g]. The curve of the nonequilibnium the rmodynamic Gibbs potential on the molar volume (Fig;. 4,a) each type of defect deformation as solitos curvature certain tcale level, characterized by a local minimum (Fig9. 4,a). Teansition of an aeom soliton curvature rn structura1 levels at the bifurcation sefs short-range osder displacements are characterized to their own local non-equilibrium Gibbs potential [9], Causing the appearance of a local minimum of the curve I7 (u).
This causes metastability deformation defects of all types. The cone equence of this is the possibility of the coexistence of o wide range ol stsuctural atates (Fig. 2). When martensieic transformations induced deformation may exisr martensitic phases with different structures. Thus, in Fig. 2 for processing cryomechanical alloy thin film Fe-Mn-C austeniee is transformed into martensite. He may have not only traditionally known BCC structure, but also the structure of the type Frank-Kasper FK12f FKt4 and FK16 (Fig. 2, d).
FK16 structure received after laser irradiation of a thining foil Fe86MnnC alloy. This X-ray diffraction pattern presents on Fig. 3,c. To identify the diffraction pattern shown Fig. 3,c we used a typical X-ray diffraction picture of compound CaCu5, having a structure of FK16 (ASTM tables).
a b
Fig. 4. Energy diagrams state of material subjected to plastic deformation: a - dépendance oa thermodynamic potential of Gibbs F (u) ffom rhe molar volume and taking) into account local bands of a hydrostatic tension of various gauge in which been arise the defective structures. Fields of various states: A - hydrostatic squeezing; B - mesosubstructures of various gauges; B1 - nanoscale structunes; C - nano structures staées; D - porosity and rracture occurrence [3]; b - potential barrier at mechanechemical reectionst XY+WZ initial state connected atoms X,Y,W,Z. The state of excited atoms XYWZ and final state with a new structure and new connections XW+ZY [10]
Fig. 4,b. illustrates the change in the energy of the system as a result of the plastic deformation. The release of energy leads to the excitation of self-propagating high-temperature synthesis in multilayer thin films structures. XY+WZ - the chemical bonds XY and WZ before the plastic defoemation. When atoms are; shuffled in and out of the equilibrium po sition, then begin to move Creely wtth energy higher than the energy ot the potential I)areiee. The emitted energy E2-E1=Q ensures continuity of the process. Thus atoms move at a speed of about several km/s.
Any excess of the yield stress generates a wave of plastic deformation [8]. Wave of plastic deformation consists of one longitudinal and two transverse modes so any shift creates turn. Such rotation is facilitated if the state of the solid becomes a liquid-like, according to the work of [11]. In the wave structure of matter corresponds to irreversible changes in the liquid phase.
Modular organization is the result of cooperative displacements of atomic groups (clusters). An example of such clusters can be packed structure which is represented as a face-centered cubic cell (Fig. 5,a). It consists of an octahedron surrounded eighth tetrahedral.
According Shal'nikov [12] liquid-like metallic phase consists of clusters if the system temperature is above 4K.
We have proposed decoding scheme similar electron diffraction using modular design elements proposed in [13]. Assembled according to the electron diffraction pattern cluster is shown in Fig. 5, ab [14]. It consists of three modules FCC lattice connected to the nucleus in the center of the tetrahedral (see Fig. 5,b). The plane (110) FCC coincides with the plane of the drawing. The scheme shows that in such a modular assembly of the vector [111] of the 1st module is almost parallel to the vector [002] of the 3rd module, etc. Each module of the FCC lattice consists of two tetrahedral and one octahedron (indicated in gray). Vectors [111] and [200] relating to the modules of different groups are parallel to each other. It is impossible to implement in a cubic crystal, but is easily
Fig. 5. The clusters structure models: a - FFCC austenite initial state; b - the formation of clusters FK12 martensite structure. Three sectional FFCC cube by diaronal plane type; 110. The center triangle is projection tetrahedral clusters of fcc-lattice [14]; c - cluster assembly consisting of icosahedra (FK12) and five octahedral (fragment of string propagation); d - the: propagatioo strings deformation martensite
implemented in a modular assembly, the center of which is tetrahedral close-packed cluster. Such modular assembly percolation way fill the space.
The modeling; of deformation martensite obtained by combination of icosahedrons (FK 122) and octahedrons. Icosahedeon it a polyhedron withteteahedral close-packed structure Frank-Kasper FK12. On Fig. 5,c the initial cluster (consists of five oclahedea and icosahedeon) is shown. On Fig. 5.d the cluster expanded with new icosahedron and octahedron is shown.
In thin film alloy samples Fe86Mn13C, subjected cryomechanical processing observed optical transitions. In Fig. 4.1 shows the spectra of the optical absorption alloy film Fe86MnnC before (lower spectrum) and after (upper spectrum) cryomechanical processing. The spectrum obtained from the film after cryomechanical processing includes sharp peaks, in contrast to the initial state of the film. We see five distinct reflections at certain wavelengths.
In Fig. 6,b shows the calculated spin-polarized electronic density of states by the scattered waves Slater fragment for clusters FK 12 connected with 5 octahedrons (fragment of string propagation), simulated by the method of Slater theory of the scattered waves. Combined density of states for spin "up" and "down" reveals the following feature: the Fermi level (EF = -0.807 Ry) falls in the region, which is characterized by a large gap in energy for spin "down" and "gap" spins "up" . This shows
Fig. 6. The comparing energy of the optical tran sitions with energy obtained from the calculation ofthe spin-polarized electron density of states for FK 12 connected with 5 octahedrons: a - optical absorption of the film Fe86Mn13C: 1 - before 2 - after cryomechanical processing, the absorption spectrum containes lines which probably are the result of exciton absorption; b - spin polarized density of eleftronic states for clusters FK 12 connected with 5 octahedrons (fragment of string propagation)
that the electron mobility for the type of structure can be limited, and this leads to the possibility of semiconducting properties.
Conclusion
In this paper, self-assembly phenomena experimentally observed crystal and magnetic structure at different levels of scale. Experimental results are compared with the concept of self-assembly structure in a solid state subjected to plastic deformation. This conception was offered in the works V.E. Panin wftlt employees.
Nature thermoelectric and magnetoresistive properties can be related to the heterogeneity of the p hase composition formed in martensitic transformations.
(Comparing the energy of the optical transitions obtained experimentally with the calculated data for the energy gaps of the electronic states with spin "up" and spin "down" for a cluster - track rod prorpstaniya come to the conclusion that they are very well coincide with the approach of the order of 0.001 P. Consequently, This theory is well confirmed by experiment, that can serve as proof of the existence of so-called rods speouting in the alloy srmples Fe86Mn13Ci kciomehanicheskoy undergoing treaiment.
Acknowledgments
The authors thank to Zhigalov V.S., Kirensky Institute of Physics Russian Academy of Sciences Si°e rian Branch, V.N. Cherepanov, AV. Nyavro Tomsk State University for ossistance.
This work was supported by a gtant № 278 from the Ministry of Science and Educatioo of the Republic Kazakhstan.
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