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3. Electric signatures of structural and chemical ordering of Heusler alloy films

Author

Dubowik, J., Goscianska, I., Zaleski, K., Kudryavtsev, Y.V., and Lee, Y.P.

Subjects
Magnetic alloys -- Properties, Magnetic alloys -- Structure, Dielectric films -- Thermal properties, Dielectric films -- Structure, Thin films -- Thermal properties, Thin films -- Structure, Business, Electronics, Electronics and electrical industries
Abstract

In this paper, we present the results of in situ temperature measurements of resistivity for some amorphous or partially crystalline Heusler alloy (HA) films: [Co.sub.2] CrAl, [Co.sub.2] MnGa, and off-stoichiometric [Ni.sub.2][Mn.sub.1+x][Sn.sub.1-x], [Ni.sub.2][Mn.sub.1+x][Ga.sub.1-x] that are known to exhibit half-metallic properties and martensitic transformations, respectively. From resistivity p versus T characteristics we distinguish various stages of chemical and structural ordering in the films. They appear to be quite distinct in both systems investigated due to differences in their electronic structure. The resistivity results are compared with magnetic characteristics for [Co.sub.2] MnGa with a high Curie temperature. High-temperature resistivity measurement is a sensitive tool for tracing the chemical and structural ordering in HA films. Index Terms--Heusler alloys (HAs), ordering, resistivity, thin films.

Published
2009

9. Martensitic transformation in Ni2MnGa films: A ferromagnetic resonance study

Author

Dubowik, J., Kudryavtsev, Y.V., and Lee, Y.P.

Subjects
Resonance -- Research, Ferromagnetism -- Research, Nickel -- Structure, Nickel -- Magnetic properties, Manganese -- Structure, Manganese -- Magnetic properties, Gallium -- Structure, Gallium -- Magnetic properties, Physics
Abstract

In this article the structure and the magnetic properties of Ni2MnGa films deposited on mica substrates, is presented and discussed. The results are discussed in terms of a qualitative model that combines the ferromagnetic resonance with a specific microstructure of the polycrystalline Ni2MnGa film.

Published
2004

12. Interfaces of Fe/Si multilayered films with a strong antiferromagnetic coupling analyzed by optical and magneto-optical spectroscopies

Author

Kudryavtsev, Y.V., Nemoshkalenko, V.V., Y.P. Lee, Kim, K.W., Rhee, J.Y., and Dubowik, J.

Subjects
Silicon compounds -- Magnetic properties, Antiferromagnetism -- Analysis, Thin films, Multilayered -- Magnetic properties, Physics
Abstract

Fe/Si multilayered films (MLF) exhibiting a strong antiferromagnetic (AF) coupling were investigated by optical and magneto-optical spectroscopies. It was shown that neither semiconducting FeSi(sub 2) nor epsilon-FeSi can be considered of the spacer layers in the Fe/Si MLF for the strong AF coupling.

Published
2001

15. Physical properties of [Ni.sub.2]MnGe alloy films with different degrees of atomic orders

Author

Kim, R.J., Lee, N.N., Kim, B.J., Lee, Y.P., Kudryavtsev, Y.V., and Kim, K.W.

Subjects
Electromagnetism -- Research, Alloys -- Research, Alloys -- Magnetic properties, Dielectric films -- Research, Dielectric films -- Magnetic properties, Thin films -- Research, Thin films -- Magnetic properties, Business, Electronics, Electronics and electrical industries
Abstract

[Ni.sub.2]MnGe alloy films were fabricated by flash-evaporation. A wide substrate temperature range (from 150 to 730 K) was chosen to prepare the alloy films with significantly different atomic orders. Various physical properties, including the magnetic, the optical, and the magnetooptical properties, were investigated. It was shown that the [Ni.sub.2]MnGe alloy film with an [L2.sub.1]-type structural order has been successfully fabricated. The ordered films exhibit the physical properties close to the corresponding bulk alloy. Unexpectedly, the disordered alloy films are not ferromagnetically ordered. These results were further analyzed in connection with the electronic structures of the alloy. Index Terms--Heusler alloy films, magnetic properties, Ni-Mn-Ge, optical properties.

Published
2005

16. A comparative study of [Ni.sub.2]MnGa, [Ni.sub.2]MnAl, and [Ni.sub.2]MnIn Heusler alloy films

Author

Kim, K.W., Kudryavtsev, Y.V., Rhee, J.Y., Lee, N.N., and Lee, Y.P.

Subjects
Alloys -- Research, Thin films -- Research, Dielectric films -- Research, Electromagnetism -- Research, Business, Electronics, Electronics and electrical industries
Abstract

Ni.sub.2]MnGa, [Ni.sub.2]MnAl, and [Ni.sub.2]MnIn alloy films were fabricated by using a flash-evaporation technique. A wide substrate temperature range (from 150 K to 720 K) was chosen to prepare the alloy films with significantly different atomic ordering. Various physical properties, including optical properties, were investigated. It was found that the optical properties of the bulk alloys are very sensitive to the atomic ordering. Unexpectedly, the disordered alloy films are not ferromagnetieally ordered. The [Ni.sub.2]MnAl bulk alloy exhibits a nonmagnetic behavior. Annealing of the disordered films restores the ordered structure with an almost full recovery of the magnetic and transport properties of the ordered films. These results were further discussed in connection with the atomic structures of the alloy films. Index Terms--Huesler alloy, Ni-Mn-Ga, Ni-Mn-In, Ni-Mn-Al.

Published
2004

17. Magnetic and structural properties of [Ni.sub.2]MnIn films

Author

Huang, M.D., Lee, N.N., Kim, B.J., Lee, Y.P., and Kudryavtsev, Y.V.

Subjects
Thin films -- Research, Dielectric films -- Research, Electromagnetism -- Research, Business, Electronics, Electronics and electrical industries
Abstract

The structural and magnetic properties of [Ni.sub.2] MnIn films deposited onto glass substrates were investigated. Two sets of films with distinct structural orders were prepared. The films deposited at an elevated temperature (730 K) have an ordered structure and are ferromagnetic, while those deposited at a low temperature (~150 K) are quite disordered (or almost amorphous) and exhibit a nonmagnetic behavior down to 5 K. However, the disordered films can restore the ordered structure as well as the ferromagnetic behavior by annealing. The results of magnetization measurements are also presented. Index Terms--Magnetic property, [Ni.sub.2]MnIn film, structural order.

Published
2004

19. Magnetic and optical properties of ordered and disordered B2-phase Co-Al alloys

Author

Rhee, J.Y., Kudryavtsev, Y.V., Kim, K.W., and Lee, Y.P.

Subjects
Aluminum compounds -- Magnetic properties, Aluminum compounds -- Optical properties, Aluminum compounds -- Spectra, Physics
Abstract

The magnetic properties and the optical conductivity spectra of the ordered and disordered Co(sub 1-x) Al(sub x) (x=0.5,0.46, and 0.38) alloy films were measured. The ordered off-stoichiometric alloy films exhibit a ferromagnetic behavior and the magnetic property is enhanced when the disorderedness is introduced.

Published
2000

20. Martensitic transformation in Ni[sub 2]MnGa films: A ferromagnetic resonance study.

Author

Dubowik, J., Kudryavtsev, Y.V., and Lee, Y.P.

Subjects
*POLYCRYSTALS, *THIN films, *MICA crystals, *STOICHIOMETRY, *MARTENSITIC transformations, *PHYSICS
Abstract

Off-stoichiometric Ni[sub 2]MnGa polycrystalline films, deposited by the flash-evaporation technique on the heated mica substrates, show a martensitic phase transformation at 310 K. At room temperature, the films have a tetragonal structure (a=b=0.598 nm, c=0.576 nm) close to the bulk Ni[sub 2]MnGa with c/a=0.96. The austenite to martensite transformation brings about an anomalous minimum in the effective magnetization and a strong increase in the ferromagnetic resonance linewidth in the martensitic phase just below the transformation temperature. The results are discussed in terms of a qualitative model that combines the ferromagnetic resonance response with a specific microstructure of the polycrystalline Ni[sub 2]MnGa film. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2004
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22. Electronic structure, optical, and magneto-optical properties of [Co.sub.2]CrGa Heusler alloy films: experimental and theoretical study

Author

Kudryavtsev, Y.V., Uvarov, N.V., Iermolenko, V.N., and Dubowik, J.

Subjects
Chromium alloys -- Magnetic properties, Chromium alloys -- Optical properties, Chromium alloys -- Electric properties, Cobalt -- Magnetic properties, Cobalt -- Optical properties, Cobalt -- Electric properties, Critical point -- Analysis, Gallium -- Magnetic properties, Gallium -- Optical properties, Gallium -- Electric properties, Physics
Abstract

The optical and magneto-optical properties of bulk [L2.sub.1] ordered [Co.sub.2]CrGa Heusler alloy (HA) are examined below and above the Curie temperature and are explained in terms of the band structure. The studies have shown that unlike bulk [L2.sub.1]-type ordered [Co.sub.2]CrGa HA sample, B2 structure order of [Co.sub.2]CrGa HA films have displayed negative temperature coefficient of resistivity.

Published
2010

23. Optical properties of Co silicides: experiment and density functional theory

Author

Kudryavtsev, Y.V., Oksenenko, V.A, Rhee, J.Y., and Y.D. Kim

Subjects
Cobalt -- Structure, Cobalt -- Electric properties, Cobalt -- Mechanical properties, Silicides -- Structure, Silicides -- Electric properties, Silicides -- Mechanical properties, Density functionals -- Analysis, X-rays -- Diffraction, X-rays -- Observations, Physics
Abstract

The dielectric functions of [Co.sub.2]Si, CoSi and Co[Si.sub.2] compounds are measured using density functional theory and compared with the calculated ones. The changes found in the optical conductivity (OC) spectra are described by using simple joint-density-of-states (JDOS) effects in the DOS curves.

Published
2007

24. Peculiarities in the electronic band structures of Cr/Cu multilayered nanostructures and [Cr.sub.(1-x)][Cu.sub.x] metastable alloy films: Ab initio linearized-augmented plane-wave and experimental optical studies

Author

Kudryavtsev, Y.V., Uvarov, V.N., Oksenenko, V.A., Lee, Y.P., and Kim, J.B.

Subjects
Copper alloys -- Structure, Copper alloys -- Optical properties, Infrared spectroscopy -- Analysis, Magnetization -- Analysis, Dielectric films -- Structure, Dielectric films -- Optical properties, Thin films -- Structure, Thin films -- Optical properties, X-rays -- Diffraction, X-rays -- Analysis, Physics
Abstract

Cr/Cu metastable alloy films (MAF) and Cr-Cu alloy films were prepared, and the peculiarities of their electronic structures were studied using optical Magneto optical spectroscopy. The comparison between experimental and modeled optical properties of the fabricated films enabled to conclude that the interfacial alloy regions of about 1.6-2.2 nm in thickness are spontaneously formed during the Cr/Cu MLF fabrication.

Published
2006

25. Structural dependence of some physical properties of the [Ni.sub.2]MnGe Heusler alloy films

Author

Oksenenko, V.A., Trofimova, L.N., Petrov, Yu.N., Kudryavtsev, Y.V., Dubowik, J., and Y.P. Lee

Subjects
Nickel compounds -- Structure, Nickel compounds -- Magnetic properties, Nickel compounds -- Optical properties, Germanium -- Structure, Germanium -- Magnetic properties, Germanium -- Optical properties, Government, Sociology and social work
Abstract

Structural ordering of the flash-evaporated [Ni.sub.2]MnGe Heusler alloy films is studied by magneto-optical (MO), optical, and magnetic methods. The optical and MO properties of [Ni.sub.2]MnGe with L[2.sub.1] structure is proved almost the same as those of [Ni.sub.2]MnGa and [Ni.sub.2]MnIn.

Published
2006

26. Effect of structural disorder on some physical properties of the Cu2MnAl Heusler alloy films

Author

Kudryavtsev, Y.V., Oksenenko, V.A., N.N. Lee, Y.P. Lee, J.Y. Rhee, and Dubowik, J.

Subjects
Crystallization -- Analysis, Polarization (Electricity) -- Analysis, Manganese alloys -- Magnetic properties, Manganese alloys -- Optical properties, Manganese alloys -- Structure, Copper alloys -- Magnetic properties, Copper alloys -- Optical properties, Copper alloys -- Structure, Physics
Abstract

The structural dependence of the magnetic, transport, optical, and magneto-optical (MO) properties of Cu2MnAl Heusler alloy (HA) thin-film samples is investigated. A significant influence of the structural disorder on the optical and magneto-optical properties of Cu2MnAl is observed and discussed in terms of the electronic structure of the alloy.

Published
2005

29. Influence of structural transition on transport and optical properties of Ni2MnGa alloy

Author

Zhou, Y., Jin, Xuensong, Xu, Huibin, Kudryavtsev, Y.V., Rhee, J.Y., and Lee, Y.P.

Subjects
Martensitic transformations -- Research, Physics
Abstract

A study was conducted to investigate the transport and optical properties of Ni2MnGa alloy in the martensitic and austenitic states. The temperature dependence of temperature coefficient of resistivity (TCR) shows a twist at the structural and ferroparamagnetic transitions.

Published
2002

30. Modified physical properties by ion-beam mixing of Fe-Si multilayered films

Author

Park, J.S., C.O. Kim, Lee. Y.P., Kudryavtsev, Y.V., Dubowik, J., Rhee, J.Y., and Szymanski, B.

Subjects
Silicon compounds -- Chemical properties, Iron compounds -- Chemical properties, Thin films, Multilayered -- Research, Ion bombardment -- Research, Physics
Abstract

The influence of ion-beam treatment on the structure and the physical properties of the Fe-Si multilayered films by using both volume- and surface-sensitive experiment tools are presented. Magnetic, magneto-optical, optical and structural studies found IBM results in a formation of metastable B2-phase Fe2Si with a perfect crystalline structure, a low coercivity and a Curie temperature of about 550 K.

Published
2002

35. Theoretical investigation of van der Waals forces between solid surfaces at nanoscales

Author

Kudryavtsev, Y.V., Gelinck, E.R.M., Fischer, H.R., and TNO Industrie en Techniek

Subjects
Silicon, Topography, Liquid layer, Silicon oxides, Oxide layer, Nano-scale roughness, Pressure effects, Surface topography, Van der Waals forces, Height distribution, Theoretical investigations, Materials, Adsorbed water, Surface structure, Solid silicon, Solid surface, Liquids, Nanostructured materials, Surface structure, morphology, roughness, and topography, Order of magnitude, Dielectric properties, Semi-empirical models and model calculations, Nano scale, Surface morphology, Surface density
Abstract

A theoretical investigation of van der Waals forces acting between two solid silicon surfaces at separations from zero to approximately 20 nm is presented. We focused our efforts on the analysis of different factors that can cause deviations from the classical pressure-distance dependence p ∼ 1/D3. It is demonstrated that a layer (oxide or water) at any of the surfaces influences the pressure up to distances, which are an order of magnitude larger than its own thickness. A jump on the p(D) curve is expected at contact of the adsorbed liquid layers. The retardation of van der Waals forces at 5 < D < 20 nm has the similar effect on the pressure as 1 nm oxide layers. At the far end of this range the pressure decreases by 30% due to the retardation. Nanoscale roughness plays a great role when the surfaces are close-to-contact, the crucial factor is the height distribution of asperities. However, their curvature and surface density are also important, as well as the amount of adsorbed water. © 2009 Elsevier B.V. All rights reserved.

Published
2009

36. Effect of short-range order on magnetic and transport properties of Fe2MnGa Heusler alloy films.

Author

Kudryavtsev, Y.V., Melnyk, A.K., Trachevskyi, V.V., Gościańska, I., and Dubowik, J.

Subjects
*MAGNETIC properties of Heusler alloys, *PHASE transitions, *TRANSPORT properties of metal
Abstract

Fe 56 Mn 20 Ga 24 , Fe 46 Mn 35 Ga 19 and Fe 39 Mn 25 Ga 36 Heusler alloy (HA) films are investigated. It is shown that as-deposited Fe-Mn-Ga films are fine crystalline with a body-centered cubic (BCC) structure. Annealing of the films leads to the formation of a face-centered cubic (FCC) structure. The BCC to FCC transformation results in a drastic increase in the magnetization, the Curie temperature as well as in a change of the sign of temperature coefficient of resistivity from negative to positive. These effects are discussed in terms of band structures of L2 1 and L1 2 phases of stoichiometric Fe 2 MnGa HA. [ABSTRACT FROM AUTHOR]

Published
2017
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37. Ellipsometric evidence of CoSi₂ formation in Co/Si multilayer induced by thermal annealing

Author

Kudryavtsev, Y.V., Lee, Y.P., Hyun, Y.H., Pavlova, E.P., and Makogon, Y.N.

Abstract

The work aim is to demonstrate the potential of the spectroscopic ellipsometry (SE) approach to study the solid state reactions, both spontaneous and/or induced by thermal annealing, in (3.0 nm Co / 10.6 nm Si)₂₀ multilayered film (MLF). The regions with a stoichiometry close to Co₂Si are supposed to be formed spontaneously in the asdeposited Co/Si MLF. Sequential anneals of Co/Si MLF at 400, 600, and 700℃ do not produce any visible changes in their amorphous-like large-angle X-ray diffraction (HAXRD) spectra, while the SE indicates the formation of regions with a stoichiometry close to CoSi. Independently on the HAXRD results, the conclusion on the formation of CoSi₂ phase induced by annealing of Co/Si MLF at 800℃ can be confidently done on the basis of only optical study. Целью работы является демонстрация возможностей спектроскопической эллипсометрии (SE) при исследовании твердофазных реакций (как самопроизвольных, так и индуцированных) в многослойной пленке (MLF) (3,0 нм Co / 10,6 нм Si)₂₀. Предполагается, что в свежеосажденной области Co/Si MLF самопроизвольно образуются области со стехиометрией, близкой к Co₂Si. Последовательный отжиг Co/Si MLF при 400, 600 и 700℃ не вызывает видимых изменений в спектрах широкоугловой дифракции рентгеновских лучей (HAXRD), в то время как SE выявляет образование областей со стехиометрией, близкой к CoSi. Независимо от результатов HAXRD, на основании только оптических исследований можно сделать надежный вывод об образовании фазы CoSi₂ под влиянием отжига Co/Si MLF при 800℃. Метою роботи є демонстрацiя можливостей спектроскопiчної елiпсометрiї (SE) при дослiдженнi твердофазних реакцiй (як спонтанних, так i iндукованих) у багатошаровiй плiвцi (MLF) (3,0 нм СО/10,6 нм Si)₂₀. Припускається, що у свiжоосадженiй областi Co/Si MLF спонтанно утворюються областi зi стехiометрiєю, близькою до Co₂Si. Послiдовний вiдпал Co/Si MLF при 400, 600 i 700℃ не викликає видимих змiн у спектрах ширококутової дифракцiї рентгенiвських променiв (HAXRD), у той час як SE виявляє утворення областей зi стехiометрiєю, близькою до CoSi. Незалежно вiд результатiв HAXRD, на пiдставi тiльки оптичних дослiджень можна зробити надiйний висновок про утворення фази CoSi₂ пiд впливом вiдпалу Co/Si MLF при 800℃.

Published
2005

39. Ferromagnetic resonance evidence of spinodal decomposition of Nix Cu1 − x (0.5 < x < 1) alloy films.

Author

Kudryavtsev, Y.V., Melnyk, A.K., Kravets, A.F., Trachevskyi, V.V., and Korenivski, V.

Subjects
*THIN film research, *FERROMAGNETIC resonance, *SUBSTRATES (Materials science), *FERROMAGNETIC materials, *MAGNETIC fields
Abstract

Films of diluted ferromagnetic (FM) Ni x Cu 1 − x alloys with 0.5 < x < 1 of about 80 nm in thickness were deposited at room temperature on glass–ceramic substrates using electron-beam co-deposition from Cu and Ni sources. The temperature dependence of the ferromagnetic resonance (FMR) spectra was investigated in the 140 < T < 500 K temperature range. The FMR spectra for films of composition 0.75 ≤ x ≤ 0.89 show two absorption peaks, which can be ascribed to a formation of two different FM phases as a result of phase separation in the alloy. The observed unusual temperature dependence of the resonance magnetic fields is interpreted as potentially magnetostrictive in nature. The results are discussed and compared to those for similar Ni–Cu films obtained using magnetron sputtering. [ABSTRACT FROM AUTHOR]

Published
2016
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