reprint

Part of Topical Section onNanoscaled Magnetism and Applications

Optically transparent magnetic andelectrically conductive Fe–Cr–Zrultra-thin films

D. V. Louzguine-Luzgin*,1, S. V. Ketov1, J. Orava1,2, and S. Mizukami1

1 Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Katahira 2-1-1, Aoba-Ku, Sendai 980-8577, Japan2Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS,United Kingdom

Received 24 September 2013, revised 19 January 2014, accepted 23 January 2014Published online 19 February 2014

Keywords conductivity, magnetism, metallic glass, nanostructure, optical properties

* Corresponding author: e-mail dml@wpi-aimr.tohoku.ac.jp, Phone: þ081 (22) 217-5957, Fax: þ081 (22) 217-5956

The transparent magnetic thin films having a nominalcomposition of Fe75Cr15Zr10 and containing nanocrystallineBCC Fe particles embedded in a metallic glassy matrix weredeposited by a magnetron sputtering technique. The nano-particles were homogeneously distributed in the glassy matrix,which results in the appearance of ferromagnetic properties.The phase composition and microstructure of the films wereexamined by X-ray diffractometry and scanning electron

microscopy equipped with EDX spectroscopy. The magneto-optical properties of the obtained films were also studied bymagnetic circular dichroism (MCD) method. The materialobtained possesses three key properties: it is opticallytransparent in the visible-light range as well as electricallyconductive and it shows ferromagnetism, which all of these areoften mutually alternative.

� 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

1 Introduction Many dielectric and semiconductiveoxides are transparent to visible light [1], while doping andformation of oxygen vacancies improve their conductivitythe optical transmittance is not significantly degraded.Transparent conductive thin films are used, for example,as electrodes for liquid crystal displays [2]. The mostcommonly used materials for this purpose are metallicoxides, like indium tin oxide [3] or zinc oxide [4], because oftheir high electrical conductivity (resistivity is�1–10mVm)and optical transmittance for visible light frequencies(transmittance �80–90%) [5]. These oxides are highlydegenerated n-type semiconductors. However, these oxide-based transparent electrodes are prone to cracking on flexiblesubstrates and high substrate temperatures are used duringfilm deposition [6]. In future, displays may require low-costlarge-area production methods. Possible substitutes forindium tin oxide are mainly conductive polymers but the lowconductivity of polymeric transparent electrodes [7] restrictstheir applications. However, metals also become partlytransparent in thin film form [8, 9].

Magnetic transparent materials attracted significantinterest of materials science community owing to their

applications in smart windows, and computer displays. Oxidemagnetic semiconductors exhibit room temperature ferro-magnetism, for example, anatase and rutile phase of Co-dopedTiO2 [10]. Although, various ferromagnetic oxide semi-conductors have been reported so far, their ferromagnetism isa matter of debate [11]. These materials are of particularinterest for spintronic devices [12], such as spin valves.

In this paper, we report the formation of nanocrystallinebody-centered cubic (BCC) Fe nanoparticles embedded inamorphous Fe–Cr–Zr thin films and study optical, magneticand electrical properties of such films. Zr is added forstabilization of an amorphous phase [13] while Cr is added toimprove corrosion resistance [14]. We show that whilethese films, in form of thick layers, cannot compete withtransparent conductive oxides (TCOs) concerning the highoptical transmittance, the Fe–Cr–Zr in form of ultra-thinfilms combines on average compromised three key applica-tion properties, i.e., high transmittance, good electricalconductivity and are magnetically active.

2 Experimental procedure An ingot of theFe75Cr15Zr10 alloy (alloy composition is given in nominal

Phys. Status Solidi A 211, No. 5, 999–1004 (2014) / DOI 10.1002/pssa.201300560

applications and materials science

statu

s

soli

di

www.pss-a.comph

ysi

ca a

� 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

atomic percentages) was prepared by arc-melting mixtures ofpure metals of 99.9 mass% purity in an argon atmosphere.From this ingot, a target for magnetron sputtering wasprepared by mechanical cutting. Thin films of 4, 7, 14, 35, 50and 225 nm in thickness were deposited by Ar gas carriermagnetron sputtering onto pre-cleaned glassy substratescontaining 71.7 mass% SiO2, 13.1 mass% Na2O3, 9.6 mass% CaO, 4.4 mass%MgO, 0.4 mass% SO2, 0.2 mass% Al2O3

and 0.1 mass% Fe2O3.The phase composition and microstructure of the

samples were examined by X-ray diffractometry (XRD)with monochromatic CuKa radiation (Bruker D8 Advance)and scanning electron microscopy (SEM) (Hitachi S-4800)equipped with EDX spectroscopy applied to verify thecomposition of the films. X-ray photoelectron spectroscopy(XPS) was carried out using an apparatus equipped withScienta MX650 X-ray source of 0.2 kW power having theAlKa (1486.7 eV) radiation.

In order to test magneto-optical properties of theobtained samples, magnetic circular dichroism (MCD)method was used [15]. The experiments were performedin visible light, wavelength ranging from 400 to 800 nm.This method is based on the differential absorption ofcircularly polarized light, induced in a sample by a magneticfield applied parallel to the direction of light propaga-tion [16]. Electrical conductivity of the films was measuredby the four-point method. The optical transmittance of thesamples was measured by Jasco V-650 UV-Vis spectro-photometer as a difference between the light intensity passedthrough the substrate and substrate with the sample. Theoptical functions were measured using variable-angle-spectroscopic ellipsometry (VASE J. A. Woollam Co.,Inc.) in the spectral range 400–2300 nm and angle ofincidence 45–758 in 108 steps. The experimental data werefitted using multiple Lorentz oscillators. The thickness of thefilms was measured by a contact profilometer.

3 Results and discussion XRD pattern of the thinfilm of 35 nm in thickness is given in Fig. 1a. The existenceof a broad peak from about 39–498 of 2u reflects theexistence of the amorphous phase in the films while a sharppeak at about 44.52� 0.078 (Gaussian fit width 0.97� 0.17)belongs to BCC Fe superimposed on the amorphousbackground. These peaks can be quite precisely separatedby using fitting with two Gaussian functions. The broadpeak from the amorphous phase has a center of mass at43.82� 0.138 (Gaussian fit width 3.71� 0.47). From theposition of (110) peak at 44.528, though it is quite wide andweak, the lattice parameter of Fe is calculated approximatelyat 287.8 pm. Zr is insoluble in BCC Fe while Cr can form asolid solution. At the film thickness of 225 nm the broadpeak from the amorphous phase has a center of mass at44.30� 0.048 (Gaussian fit width 2.21� 0.09) (Fig. 1b),while the lattice parameter of Fe is calculated approximatelyat 286.9 pm (peak at 44.66� 0.01, Gaussian fit width0.52� 0.02), which is very close to the value of pure Feof 286.6 pm.

The volume fraction of the crystalline BCC Fe phasechanges with the sample thickness. The peak area ratiobetween that of (110) Fe and the amorphous phase changesfrom �0.22 at 35 nm thick film to �0.46 for 225 nm thickone. However, precise determination of the volume fractionof BCC Fe phase is difficult.

SEM images of the films are shown in Fig. 2. Fe particlessize is about 8, 9 and 22 nm in the samples having 14, 35 and225 nm in thickness, respectively. At lower sample thicknessit was not possible to obtain a high resolution SEM imageowing to film transmittance. An analysis of (110) peakbroadening in the X-ray diffraction patterns taking intoaccount an instrumental broadening of the machine (theprocedure is described in Ref. [17]) produced the size of thecoherent scattering area of 8.5 and 17 nm for the sampleshaving 35m and 225 nm in thickness, respectively. Thedifference in the values obtained by SEM compared tothe peak broadening in the X-ray diffraction patterns may beconnected with the lattice strain and insufficient resolution ofSEM at high magnification.

The chemical composition of the as-prepared sampleswas measured by EDX in SEM. The average chemicalcomposition of the sample of 225 nm in thickness isFe75Cr15.3Zr9.7. XPS spectroscopy of the surface layers ofthe samples indicated presence of Fe2O3, Cr2O3 and ZrO2.

Fe–Zr glassy alloys with high Zr content up to 88 at.%were produced by the melt spinning technique [18] ensuringrapid solidification with a typical cooling rates of105–106K s�1 [19, 20]. However, the effective coolingrates on physical vapor deposition (condensation onsputtering) are significantly higher, in general [21]. Whywas it not possible to obtain the amorphous single phase?

Figure 1 XRD patterns of the as-sputtered samples of (a) 35 nmand (b) 225 nm in thickness. The insert in part (a) (and also (b))shows the fitting of the first diffraction maximum with twoGaussian functions (G1 and G2).

1000 D. V. Louzguine-Luzgin et al.: Fe–Cr–Zr ultra-thin films

� 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.pss-a.com

ph

ysic

a ssp stat

us

solid

i a

This is likely connected with high atomic mobility of specieson the surface upon layer-by-layer deposition duringsputtering whereas melt solidification on casting on to arotating Cu wheel takes place almost simultaneously withinthe layer of about 20mm in thickness. On sputtering the

atoms have higher mobility on the surface which causesprimary precipitation of BCC Fe (Cr is dissolved) from theinitially amorphous matrix. The amorphous phase shouldbe enriched in Zr, which is insoluble in crystalline Fe.Nevertheless this could not be determined under the SEMexperiments. Another aspect could be connected with ratherlow surface crystallization temperature of Fe-rich glassyalloys. It was found that crystallization at the surface starts atlower temperature than in the bulk [22]. BCC Fe was foundto form at the surface layer of 300 nm thickness and neitherthe equilibrium Fe2Zr intermetallic compound nor theintermediate compounds were observed on crystallization.

The Fe–Cr–Zr films are found to be optically transparentdue to the low thickness (Fig. 3). Gradual decrease in thetransmittance at lower wavelength is caused by the startingabsorption of oxide glassy substrate, the influence of whichcannot be subtracted completely. In case of low filmthickness the sample is 90% transparent in optical diapason.The transmission spectra are smooth and do not have anycharacteristic absorption peaks, for example, like thoseobserved in Si70Ge20Mn10 films [23]. The optical transmit-tance as a function of the sample thickness at twowavelengths is shown in Fig. 4 in comparison with thefilms of pure Fe [24]. For the same thickness, the Fe–Cr–Zrfilms are more transparent than the corresponding Fe films.

The thin film samples showed rather high electricalresistivity (r) in the range of several mVm. Significantlyhigher optical transmittance of the studied Fe–Cr–Zr filmscompared to pure Fe films of the same thickness (Fig. 4)correlates well with their considerably higher electricalresistivity as shown in Fig. 5 [25]. Owing to the disorderedamorphous structure of the matrix the electrical resistivity ofFe–Cr–Zr films at the same film thickness is about an orderof magnitude higher compared to pure Fe films which in turnmay lead to significantly higher transmittance [26] byreducing the skin layer eddy currents.

Bulk electrical resistivity of Fe90Zr10 alloy at roomtemperature is 1.25mVm [27], typical for metallic glassy

Figure 2 SEM images of the as-sputtered samples of (a) 14 and (b)35 nm in thickness obtained at different magnification.

Figure 3 Optical transmittance of the Fe–Cr–Zr films as a functionof the wavelength.

Figure 4 The optical transmittance per sample thickness forFe–Cr–Zr (solid symbols) and pure Fe (open symbols) at twowavelengths 400 and 700 nm, represented by diamonds andtriangles, respectively, fitted by the exponential function.

Phys. Status Solidi A 211, No. 5 (2014) 1001

www.pss-a.com � 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Original

Paper

samples, which is close to that value extrapolated for bulkFe–Cr–Zr sample (Fig. 5). The electrical resistivity of theFe–Cr–Zr thin film shows a weak dependence on the samplethickness. The measured dependence of the resistivity as afunction of the sample thickness deviates markedly from thepredictions of the Fuchs–Sondheimer theory [28, 29]: in thestudied range of film thickness, the electrical resistivitycannot be fitted with the hyperbolic function but can be fittedwell with the second order polynomial function (Fig. 5). Thedependence of electrical resistivity of Fe films as a functionof thickness follows a power law (Fig. 5).

In general, the electrical resistivity of metallic thin filmswas found to be strongly dependent on the film thickness.In a variety of metals, for example, aluminium, cobalt,nickel, palladium, silver and gold, the electrical resistivityis inversely proportional to the film thickness [30]. Theelectrical resistivity of nanocrystalline Fe and Co obtained inthin film shape was about 1mVm in the order of magnitudeat the film thickness range of 3–30 nm [25, 31, 32].

The values of r of the Fe–Cr–Zr thin film are also not sofar from those (1–10mVm) obtained for the impurity dopedindium oxide [33], zinc oxide or tin oxide [34]. Also, itwas found that deposited pure polycrystalline metals ofapproximately 10 nm or greater thickness have a sheetresistance equivalent to or better than indium tin oxide [8].The transmittance of 80–90% observed for the thinnest Fe–Cr–Zr films is also typical for the transparent conductiveoxides [33]. However, the thickness of the transparentconductive oxides leading to such high transmittance valuescan reach hundreds of nanometers as there is no absorptionon free carriers in case of TCO in that region.

The dependence of refractive index and extinctioncoefficient on wavelength, obtained from the spectroscopicellipsometry, for three thicknesses 7, 14 and 35 nm is shownin Fig. 6. The spectroscopic ellipsometry data were fittedtogether with transmittance to improve best-fit quality; themean-square error was <5 for all samples. The refractive

index decreases with decreasing thickness of the films whichcan be characterized by a smaller density owing to smallerparticles size.

The sample interacts with the external magnetic field(H). Figure 7 shows Kerr rotation angle as a function ofthe applied magnetic field (H). The dependence showssaturation at large field of about 7 kOe with low magneticsusceptibility which is typical for ferromagnetic nanoscaledmaterials. At particles size less than 10 nm a super-paramagnetic behavior may become important as shownin Ref. [35] while it is not the case in current material.This effect may be connected with the influence of theintergranular amorphous phase. As Zr is almost insoluble inBCC Fe and the lattice parameter of the crystalline phaseis almost equal to pure iron then we can assume thatcrystalline phase is a solid solution of Cr in Fe. Chromium isknown to lower the Curie temperature (Tc) of Fe but until75 at.% does not affect iron magnetic ordering [36]. So, thecrystalline part is ferromagnetic. Adding Zr in small amountsmakes an unusual effect on magnetic ordering of Fe–Zrglasses. While at high concentrations of Zr iron magnetic

Figure 5 Electrical resistivity as a function of the film thickness forFe–Cr–Zr (diamonds), pure Fe [25] (circles) and those values forsome TCOs: In2O3:Ti (ITiO), In2O3:Mo (IMO) and In2O3:Sn (ITO)(triangles) (the values and references are given in Table 1).

Figure 6 Refractive index (solid lines) and extinction coefficient(dashed lines) dispersion for three different thicknesses ofFe–Cr–Zr thin films.

Figure 7 Kerr rotation, sample of 35 nm in thickness.

1002 D. V. Louzguine-Luzgin et al.: Fe–Cr–Zr ultra-thin films

� 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.pss-a.com

ph

ysic

a ssp stat

us

solid

i a

moment is constant, with decreasing Zr amount Curietemperature of the glass drops significantly and high fieldmagnetization curves demonstrate the presence of asubstantial noncollinear component to the magnetic orderat ultra-low temperatures [18, 37]. It appeared that forFe100�xZrx metallic glass at x¼ 10 at.% the Curie tempera-ture would be Tc¼ 226K [37]. While total Zr amount in thefilm is 10 at.% in the glassy phase it should be considerablylarger due to the primary crystalline phase formation. Thus,we assume that amorphous phase is also ferromagnetic.

Having two different soft ferromagnetic phases we couldhave noticed special features on the magnetization curveshowing different saturation magnetizations of these phases.However, one can notice that the curve is rather smooth andnot really typical to soft ferromagnetic materials. Magneti-zation saturates in very high field. So there is a magneticcoupling between crystalline and amorphous phases. SEMimages (Fig. 2) indicate that the size of particle is less than10 nm. Thus, they are either in single domain state or insuperparamagnetic state. If they are in single domain state,then with such a shape of the magnetization curve (Fig. 7)one can expect that the magnetization vector with zeroexternal magnetic field would be in plane of the film.

The properties of Fe–Cr–Zr films are summarized inTable 1 in comparison with those of Fe films [24, 25] andtransparent conductive oxides, namely In2O3:Ti (ITiO)(IMO), In2O3:Mo In2O3:Sn (ITO) and SnO2:F (FTO) [38].The Fe–Cr–Zr samples showed ferromagnetic behavior,and good optical transmittance and electrical conductivitycomparable with transparent conductive oxide films whileits magnetic response is significantly stronger than that ofMn- or Fe-doped oxides [39].

It should also be noticed that in comparison with oxidesmetallic glasses and glassy crystal composites the Fe–Cr–Zrfilms are much less brittle and tougher materials. Forexample, fracture toughness (KIc) is 10–100MPam1/2 formetallic glasses and 0.7MPam1/2 for oxide glasses [40].This property is very important for flexible displayswhich require good bend ductility and resistance to crackpropagation.

4 Conclusions Optically transparent, magnetic, amor-phous thin films containing Fe-based BCC nanoparticles of

about 10 nm in size were produced and studied in the presentwork. The film thickness ranged from 4 to 225 nm. Thetransmission spectra are smooth showing a wide-transparentwindow for visible-light frequencies. In case of low filmthickness it is 90% transparent in optical diapason likelyowing to higher electrical resistivity of the amorphous matrixphase compared to those of crystalline metals. Such hightransmittance value is close to those of transparentconductive oxides. The Fe–Cr–Zr samples showed ferro-magnetic behavior and on average compromised three keyapplication properties, i.e., high transmittance, metallicelectrical conductivity and ferromagnetism.

Acknowledgements This work was supported by WorldPremier International Research Center Initiative (WPI), MEXT,Japan. The authors sincerely thank T. Hitosugi (WPI-AIMR) forfruitful discussions and R. Kumashiro for conducting the XPSexperiments.

References

[1] A. Klein, C. Körber, A.Wachau, F. Säuberlich, Y. Gassenbauer,S. P. Harvey, D. E. Proffit, and T. O. Mason, Materials 311,4892 (2010).

[2] B. G. Lewis and D. C. Paine, MRS Bull. 25, 22 (2000).[3] H. Kim, C. M. Gilmore, A. Piqué, J. S. Horwitz, H. Mattoussi,

H. Murata, Z. H. Kafafi, and D. B. Chrisey, J. Appl. Phys. 86,6451 (1999).

[4] T. Itoh, K. Matsuyama, K. Shimakawa, J. Orava, T. Wagner,and M. Frumar, Phys. Status Solidi C 6, S110 (2009).

[5] H. Kim, C. M. Gilmore, A. Piqué, J. S. Horwitz, H. Mattoussi,H. Murata, Z. H. Kafafi, and D. B. Chrisey J. Appl. Phys. 86,6451 (1999).

[6] Y. Leterrier, L. Medico, F. Demarco, J. A. E. Manson, U.Betz, M. F. Escol, O. M. Kharrazi, and F. Atamny, Thin SolidFilms 460, 156 (2004).

[7] S. Kirchmeyer and K. Reuter, J. Mater. Chem. 15, 2077(2005).

[8] B. O’Connor, C. Haughn, K.-H. An, K. P. Pipe, and M.Shtein, Appl. Phys. Lett. 93, 223304 (2008).

[9] H. Klauk, J. R. Huang, J. A. Nichols, and T. N. Jackson, ThinSolid Films 366, 272 (2000).

[10] Y. Matsumoto, M. Murakami, T. Shono, T. Hasegawa,T. Fukumura, M. Kawasaki, P. Ahmet, T. Chikyow,S. Koshihara, and H. Koinuma, Science 291, 854 (2001).

[11] S. A. Chambers and R. F. C. Farrow, MRS Bull. 28, 729(2003).

[12] H. Ohno, Nature Mater. 9, 952 (2010).[13] Z. Altounian, E. Batalla, and J. O. Strom-Olsen, J. Appl. Phys.

59, 2364 (1986).[14] M. F. Ashby and D. R. H. Jones, Engineering Materials 2

(with ed. corrections) (Pergamon Press, Oxford, 1992), chap12, p. 119.

[15] P. J. Stephens, Annu. Rev. Phys. Chem. 25, 201 (1974).[16] D. Caldwell, J. M. Thorne, and H. Eyring, Annu. Rev. Phys.

Chem. 22, 259 (1971).[17] D. V. Louzguine and A. Inoue, JIM Mater. Trans. 39, 245

(1998).[18] D. H. Ryan, J. O. Strom-Olsen, R. Provencher, and

M. Townsend, J. Appl. Phys. 64, 5787 (1988).[19] H. S. Chen and D. Turnbull, J. Chem. Phys. 48, 2560 (1968).

Table 1 Thickness (d), transmittance (T) at wavelength l¼ 400and 700 nm, electrical resistivity (r) and ferromagnetism (M) ofFe–Cr–Zr, Fe and transparent conductive oxide films.

d(nm)

T400

(%)T700

(%)r(mVm)

M Ref.

Fe–Cr–Zr 4 84 89 �9a þ –

Fe 3 55 70 1.8 þ [24]ITiO 250 72.5 80 1.9 � [38]IMO 200 75 85 1.6 � [38]ITO 120 85 84 1.3 � [38]FTO 415 80 84 3.9 � [38]

aExtrapolated.

Phys. Status Solidi A 211, No. 5 (2014) 1003

www.pss-a.com � 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Original

Paper

[20] D. V. Louzguine-Luzgin and A. Inoue, J. Nanosci. Nano-technol. 5, 999 (2005).

[21] T. W. Barbee, Jr., W. H. Holmes, D. L. Keith, M. K. Pyzyna,and G. Ilonca, Thin Solid Films 45, 591 (1977).

[22] M. Fujinami and Y. Ujihira, Hyperfine Interact. 27, 301(1986).

[23] D. V. Louzguine-Luzgin, P. Sharma, M. Fukuhara, A.Dmytruk, and A. Inoue, J. Nanosci. Nanotechnol. 9, 5865.(2009).

[24] E. Valkonen, B. Karlsson, and C.-G. Ribbing, Sol. Energy 32,211 (1984).

[25] M. Rubinstein, F. J. Rachford, W. W. Fuller, and G. A. Prinz,Phys. Rev. B 37, 8689 (1988).

[26] R. M.Mutiso, M. C. Sherrott, A. R. Rathmell, B. J. Wiley, andK. I. Winey, ACS Nano 7, 7654 (2013).

[27] L. Fernández Barquín, J. C. Gómez Sala, P. D. Babub, andS. N. Kaul, J. Magn. Magn. Mater. 133, 82 (1994).

[28] K. Fuchs, Proc. Cambr. Phil. Soc. 34, 100 (1938).[29] E. H. Sondheimer, Adv. Phys. 1, 1 (1952).[30] J. W. C. de Vries, Thin Solid Films 167, 25 (1988).

[31] G. I. Frolov, O. A. Bayukov, V. S. Zhigalov, L. I. Kveglis, andV. G. Myagkov, JETP Lett. 61, 63 (1995).

[32] V. S. Zhigalov, G. I. Frolov, and L. I. Kveglis, Phys. SolidState 40, 1878 (1998).

[33] S. Calnan and A. N. Tiwari, Thin Solid Films 518, 1839 (2010).[34] K. Ellmer, J. Phys. D, J. Appl. Phys. 34, 3097 (2001).[35] D. V. Louzguine-Luzgin, T. Hitosugi, N. Chen, S. V. Ketov,

A. Shluger, V. Yu. Zadorozhnyy, A. Caron, S. Gonzales, C. L.Qin, and A. Inoue, Thin Solid Films 531, 471 (2013).

[36] E. G. Moroni and T. Jarlborg, Phys. Rev. B 47, 3255 (1993).[37] D. H. Ryan, J. M. D. Coey, E. Batalla, Z. Altounian, and

J. O. Strom-Olsen, Phys. Rev. B 35, 8360 (1987).[38] S. Calnan, H. M. Uphadhyaya, S. Buecheler, G. Khrypunov,

A. Chirila, A. Romeo, R. Hashimoto, T. Nakada, andA. N. Tiwari, Thin Solid Films 517, 2340 (2009).

[39] B. B. Straumal, S. G. Protasova, A. A. Mazilkin, T. Tietze,E. Goering, G. Schütz, P. B. Straumal, and B. Baretzky,Beilstein J. Nanotechnol. 4, 361 (2013).

[40] A. L. Greer, Y. Q. Cheng, and E. Ma, Mater. Sci. Eng. R 74,71 (2013).

1004 D. V. Louzguine-Luzgin et al.: Fe–Cr–Zr ultra-thin films

� 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.pss-a.com

ph

ysic

a ssp stat

us

solid

i a