Pt trilayer films under EUV irradiation

Nuclear Instruments and Methods in Physics Research B 364 (2015) 33–39

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Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb

Structural investigation of ultrathin Pt/Co/Pt trilayer films under EUV irradiation E. Dynowska a,⇑, J.B. Pelka a, D. Klinger a, R. Minikayev a, A. Bartnik c, P. Dluzewski a, M. Jakubowski a, M. Klepka a, A. Petruczik a, O.H. Seeck d, R. Sobierajski a, I. Sveklo b, A.A. Wawro a, A. Maziewski b a

Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, PL-02-668 Warsaw, Poland Faculty of Physics, University of Białystok, ul. L. Ciolkowskiego, 15-245 Białystok, Poland Institute of Optoelectronics, Military University of Technology, ul. S. Kaliskiego 2, 00-908 Warsaw, Poland d DESY, Nottke Str. 85, 22607 Hamburg, Germany b c

a r t i c l e

i n f o

Article history: Received 29 January 2015 Accepted 27 July 2015 Available online 26 August 2015 Keywords: Synchrotron radiation Pt/Co/Pt films Structural characterization

a b s t r a c t Trilayer systems containing ultrathin (3 nm) cobalt layer grown on 5 nm thick Pt buffer layer and covered with 3 nm thick Pt cap layer grown at room temperature by molecular beam epitaxy on the Al2O3(00.1) substrate have been irradiated by nanosecond extreme ultraviolet light pulses. It was previously evidenced that light irradiation induced irreversible change of direction of magnetization in such nanostructures. In order to understand the reasons of such behavior the structural studies with the use of X-ray diffraction and transmission electron microscopy of the as-grown and irradiated samples have been done. It was found that irradiation leads to intermixing of cobalt with platinum giving rise to creation of Pt1xCox disordered alloy. The methodology of determination of the strain state of the layers, relaxed lattice parameter of the unit cell and the composition of Pt1xCox alloys has been developed and described in details. The results of structural studies of the as grown Pt/Co/Pt nanostructures as well as those modified by irradiation are presented in this paper. Ó 2015 Elsevier B.V. All rights reserved.

1. Introduction Magnetic thin films and multilayers with perpendicular magnetic anisotropy are very interesting research objects, due fundamental research of novel properties and potential applications in areas such as ultrahigh density magnetic recording, permanent magnetism, and magneto-optical memory storage devices. In particular, ferromagnetic thin films grown on Pt attract great attention in magnetic nanostructure research. In this system different interesting phenomena, such as enhanced magneto-optic effect [1,2], induced magnetic moment [3,4], extraordinary Hall effect [5], etc have been observed. Moreover, the presence of perpendicular magnetization caused further research activities on topics of the magnetic anisotropy [6,7], spin reorientation transition [8] and magnetic domains [9,10]. One of the most intensively studied system is Pt/Co owing enhanced magneto-optical response in the ultraviolet range [11]. Magnetic anisotropy in Pt/Co systems can be controlled with different parameters such as Co film thickness or sample’s ⇑ Corresponding author. E-mail address: [email protected] (E. Dynowska). http://dx.doi.org/10.1016/j.nimb.2015.07.116 0168-583X/Ó 2015 Elsevier B.V. All rights reserved.

temperature. It is important to find methods for local changes of magnetic, magnetooptical sample properties, pattering. Ion beam or light irradiations are used for these purposes. It was been shown by Chappert et al. [12] that 30 keV He+ ions irradiation can reduce magnetic anisotropy for thin Co films and magnetisation rotate to in-plane state without visible change of surface morphology. Structural studies [13,14] show that irradiation destroyed Co/Pt interface inducing substitutional mixing maintaining the initial crystallographic structure but reducing magnetic anisotropy. Later, for thick Co layers, it was demonstrated increase of magnetic anisotropy under 30 keV Ga+ ion irradiation [15,16]. Structural study [17] claims that the increase of magnetic anisotropy is correlated with increase of surface strain under irradiation. Modification of magnetic anisotropy with intense short laser’s pulses is also possible. Nanoseconds range laser annealing without ordered alloy formation was done for multilayer (0.3 nm Co)/(0.8 nm Pt) film [18]. As a result, magnetic saturation is increased by 10% while effective magnetic anisotropy is decreased by about 50%. The appearance of new wide XRD reflection indicates on Co–Pt alloy formation. For thicker Co films femtosecond pulse laser irradiation can induce increase of magnetic anisotropy [19].

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Similar effect induced by extreme ultraviolet (EUV) light pulses also exists in Pt/Co/Pt. Results of structural studies of the as grown and EUV modified nanostructures Pt/Co/Pt are the subject of this paper. 2. Experimental The trilayer systems containing ultrathin (3 nm) cobalt layer grown on 5 nm thick Pt buffer layer and covered by 3 nm thick cap layer of Pt have been prepared by molecular beam epitaxy (MBE) method on the single crystal Al2O3(00.1) substrate at room temperature. In-plane magnetization ordering was observed at as-grown samples. Such nanostructures were irradiated with extreme ultraviolet (EUV) pulses from plasma source operating with gas target Kr/Xe/He excited with 0.8 J Nd:YAG 10 Hz laser [20]. The EUV radiation was focused using a gold-plated grazing incidence ellipsoidal collector (Rigaku Innovative Technologies Europe s.r.o.), allowing for efficient focusing of radiation in k = 9  70 nm wavelength range. The most intense emission from the Kr/Xe plasma, was in a relatively narrow spectral region, centered at k = 11 ± 1 nm. The spectral intensity at longer wavelengths was much smaller, however, spectrally integrated intensities in both ranges were comparable. The EUV fluence in a focal plane of the collector reached 0.05 J/cm2 in the center of the focal spot. Spot half-maximum diameter 0.8 mm was used. Power fluence was enough to induce out-of-plane magnetization ordering inside EUV illuminated spots. Two types of EUV irradiated samples were prepared. First, samples with separated spots, consisting of non-overlapping EUV spots obtained after N = 10, 100, and 1000 accumulated pulses. Second, quasi-uniform samples, obtained after spot-by-spot EUV irradiation with sample raster scanning with a step of 0.4 mm; each spot was irradiated with N = 30 accumulated pulses. Single spot samples were used for TEM and micro-beam XRD measurements, while

quasi-uniform samples were used for conventional XRD measurements. The structural characterization has been done by X-ray diffraction (XRD) methods with use of the micro-beam synchrotron radiation of k = 1.23984 Å at the P-08 beamline of Petra III at DESY as well as the laboratory diffractometer (Philips X’Pert MPD Pro Alpha1, Cu Ka1 radiation of k = 1.540598 Å). In this instrument, the classical Bragg–Brentano geometry is modified through installation of a Johansson Ge(111) monochromator in the incident beam and a linear semiconductor strip detector. The morphology of the samples was examined by transmission electron microscopy methods (TEM) using FEI Titan CUBED 80-300 microscope operating at 300 kV acceleration voltage. The cross sectional specimens were prepared with the use of FIB method. 3. Results and discussions 3.1. Transmission electron microscopy TEM studies showed a cross-section of the as-grown and irradiated sample (Fig. 1). The image of as-grown sample is presented in the Fig. 1a. We can clearly see a brighter band of the cobalt film between platinum buffer and cover layers seen as two darker stripes. The TEM image of the irradiated sample (Fig. 1c) shows rather homogeneous gray layer formed by mixing the cobalt and platinum layers. In both cases, as-grown and irradiated samples, the layers have a crystalline structure with a preferential orientation in the respect to the substrate surface. 3.2. X-ray diffraction 3.2.1. As-deposited samples–results of measurements Fig. 2a shows the diffraction pattern performed in a wide range of 2h angles for the as grown Pt (3 nm)/Co(3 nm)/Pt(5 nm)/Al2O3

(c)

(b) FIB- protected layer

(a)

cap layer Pt Co buffer Pt

substrate Al2O3 Fig. 1. TEM images of Pt(3 nm)/Co(3 nm)/Pt(5 nm) trilayer: (a) as grown, (c) after irradiation. Relative scheme of the sample with named layers is shown in (b).

(a)

00.6 Al2O3

(b)

λ = 1.540598 A 00.6 Al2O3

1000000

Intensity (counts)

Intensity (counts)

00.12 Al2O3

λ = 1.540598 A

1000000

100000

10000 Co 1000

Thickness frienges

100000

10000

Co d = 2.088 A

1000 Pt 111 d = 2.273 A

100

30

40

Pt 111 d = 2.273 A

Pt 222 d = 1.136 A 50

60

2θ (deg)

70

80

90

100 100

25

30

35

40

45

50

2θ (deg)

Fig. 2. The diffraction patterns of the as grown Pt(3 nm)/Co(3 nm)/Pt(5 nm) trilayer performed with the use of conventional diffractometer: (a) symmetrical 2h-x scan, (b) the zoom of this scan in the vicinity of 1 1 1 Pt peak.

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1000000

1E7

(a)

(b)

00.12 Al2O3

1000000

Intensity (counts)

Intensity (counts)

00.6 Al2O3

100000

10000

222 Pt d = 1.133 A

Co d = 2.064 A

1000

100

00.12 Al2O3

00.6 Al2O3

222 Pt d = 1.130 A

100000

10000

Co d = 2.078 A

1000 111 Pt d = 2.266 A

35

40

45

100

50

55

60

65

70

75

80

85

90

95 100

111 Pt d = 2.260 A 35

40

45

50

55

60

2θ (deg)

65

70

75

80

85

90

95 100

2θ (deg)

Fig. 3. Symmetrical 2h-x diffraction patterns of the as-grown: (a) Pt(3 nm)/Co(3 nm)/Pt(10 nm) and (b) Pt(3 nm)/Co(3 nm)/Pt(33 nm) trilayers.

trilayer. Besides the very strong reflections from the substrate the 1 1 1 and 2 2 2 Pt layers peaks are well developed as well. In the vicinity of 1 1 1 reflection (Fig. 2b) several peaks originating from the finite thickness of the trilayer – so called Kiessig oscillations (thickness fringes, or Laue oscillations) – are visible. Similar result has been obtained for magnetron sputtered Pt (3.4 nm)/Co (1.3 nm)/Pt (4 nm)/Al2O3 [21]. These oscillations indicate large coherence length of Pt atomic layers in the direction normal to the layer’s plane. Such fringes are symmetrically distributed around the position of diffraction peaks from the Pt and Co layers. However, if the thickness of the layers are relatively small (our case) the Kiessig oscillations prevent the direct observation of the respective diffraction peaks. Despite this it is possible to determine the position of 1 1 1 Pt diffraction peak which should be placed in the centre between two strongest fringes, as shown in the Fig. 2b. In a similar manner the position of the 1 1 1 Co peak has been estimated (see Fig. 2). The correctness of this interpretation confirms the position of well distinguished 2 2 2 Pt peak because the thickness fringes around this peak are evidently weaker than those in the vicinity of 1 1 1 peak (see Fig 2a). The lattice spacing d111 calculated from the presumed position of the 1 1 1 Pt peak is equal to 2. 273 Å and the d222 value calculated from the real position of 2 2 2 Pt peak is 1.136 Å. The obtained d-values are larger than those determined for the bulk Pt and Co. Such shift can be caused by compressive stress in the layers. Generally, the lattice mismatch between Pt and sapphire is very large (42%). However, the second-neighbor Pt atoms form a hexagon which is only 0.9% larger than hexagon of the sapphire. Thus the epitaxial relationship between sapphire substrate and Pt layer can be determined as follows: Pt[1 1 1]kAl2O3[00.1], and Pt(1 1 0)kAl2O3(10.0) [22]. Such construction explains compressive strain of thin Pt layers. Additionally, two other investigated samples have been prepared to determine the influence of the Pt buffer thickness on structural parameters of individual layers and resulting diffraction patterns. These samples differed from the previous one only in the thickness of the Pt buffer layers which were 10 nm and 33 nm thick, respectively. The results are shown in the Fig. 3. The differences are clear – the thickness fringes are relatively weaker and direct observation of the both diffraction peaks from Pt layers, 1 1 1 and 2 2 2, is possible. Moreover, the values of d111 and d222 lattice spacing are smaller than those from thin buffer. However, surprisingly the lattice spacing in the growth direction decreases with increasing of the Pt layer thickness (d111 = 2.266 Å for 10 nm thick buffer and d111 = 2.260 Å for 33 nm thick buffer – see Fig. 3a and b). The explanation of this behavior may be possible after determination of the stress state of the layers.

3.2.2. Methodology of the determination of isotropic biaxial stress state and relaxed lattice parameters The measurements of at least two diffraction peaks, symmetrical and asymmetrical are necessary to determine of the stress state of Pt layers for isotropic biaxial stress model. In the fcc unit cell the position of atoms in the (1 1 1) plane have a hexagonal symmetry similarly as in the hcp structure. In the case of cubic [1 1 1] growth direction the transformation to the hexagonal or rhombohedral cells is needed for application of isotropic biaxial stress model. The transformation of the fcc unit cell to the hexagonal one was done according the formula:

ahex

pffiffiffi pffiffiffi 2 ¼ acub and c ¼ acub 3 2

ð1Þ

The lattice parameter value of bulk Pt is acub = 3.923 Å [23]. The lattice parameters of the transformed hexagonal cell are equal to: ahex = 2.7740 Å, c = 6.7948 Å and the ratio c/a = 2.45. If c/a is larger than 2.45 the cubic unit cell is under compressive stress, while for tensile stress of the cubic cell c/a is smaller than 2.45. The determination of the strain state and the relaxed lattice parameters of the Pt layers were done on the base of the lattice spacing values calculated from the symmetrical 2 2 2 and asymmetrical 1 1 3 cubic reflections. The positions of these reflections were corrected basing on the relevant reflections from the Al2O3 substrate as it is seen in Fig. 4a–c. These reflections correspond to 00.6 and 11.3 reflections in hexagonal cell, respectively. The lattice parameters of hexagonal cell are obtained by solving the system of equations proper for hexagonal structure:

1 2

dhkl

2

2

4 h þ hk þ k ¼ 3 a2

!

2

þ

l c2

ð2Þ

So having two lattice spacings for two different peaks we can derive a and c values. In the next step the volume of the hexagonal unit cell is calculated from the formula: Vhex = 0.866 a2c, and the volume of the strained cubic cell from the relation: Vcub = 1.3333 Vhex. The relaxed lattice parameter of cubic cell can be estimated as pffiffiffiffiffiffiffiffiffi ¼ 3 V cub , assuming that after relaxation this volume is arelaxed cub preserved. The fcc unit cell can be also transformed to the rhombohedral cell which is described by two lattice parameters ar and a, where ar = a = b = c, a = b = c – 60°. If the cubic cell is not deformed then pffiffiffi pffiffiffi 2 and a = 60°. For a deformed cubic cell ar – acub 2 and ar ¼ acub 2 2 a < 60° or a > 60° are for compressive or tensile stresses in the growth plane, respectively.

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(a)

Intensity (counts)

1000000

11.12 Al2O3

10.10 Al2O3

100000

10000 222 Pt

1000

113 Pt

100

70

75

80

85

90

95

2θ (deg)

(b) 10.10 Al2O3

100000

00.12 Al2O3

(c)

00.12 Al2O3 1000000

Intensity (counts)

Intensity (counts)

10.10 Al2O3 10000 222 Pt

1000

113 Pt

222 Pt

100000

10000

100

113 Pt 1000

100

10

10 70

75

80

85

90

95

70

75

2θ (deg)

80

85

90

95

2θ (deg)

Fig. 4. The 2h-x symmetrical (2 2 2 Pt and 00.12 Al2O3) and asymmetrical (1 1 3 Pt and 10.10 Al2O3) diffraction patterns of the as deposited trilayers: (a) Pt(3 nm)/Co(3 nm)/ Pt(5 nm), (b) Pt(3 nm)/Co(3 nm)/Pt(10 nm) and (c) Pt(3 nm)/Co(3 nm)/Pt(33 nm).

The lattice parameters of the rhombohedral cell can be calculated from the known parameters of the hexagonal cell as follows:

ar ¼

1 3

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 3a2H þ c2 ;

sin

a 2

3 ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 3 þ ðc=aÞ2

ð3Þ

The Pt lattice constants (determined for studied trilayer samples) are given in the Table 1. They show that stress state of Pt layers decreases with increasing thickness of the buffer – for thickest buffer (33 nm) the layer is almost completely relaxed. Unexpected results concern the relaxed lattice parameters of Pt layers: for the thinnest buffer arelaxed is slightly larger from that of bulk Pt (aPt = 3.923 Å) while for the thicker buffers this value clearly decreases. At the moment we are not able to clarify this effect – we suppose that it can be a result of a specific structural defects created during the growth of the layers. The final explanation of this problem needs further studies.

3.2.3. EUV Irradiated samples Out-of-plane magnetization state was observed in Pt(3 nm)/Co(3 nm)/Pt(5 nm) trilayers structures with EUV irradiated separate spots and quasi-uniform samples. The X-ray diffraction measurements at the separated spots were performed with the use of the micro-beam synchrotron radiation. Unfortunately, due to technical reasons, the measurements for 2h angles higher than 50° were not possible therefore only diffraction patterns in the vicinity of 1 1 1 Pt reflections are shown in Fig. 5. In consequence, an interpretation of these diffraction patterns was based on the (1 1 1) lattice spacing (in the growth direction) preventing the determination of the stress state and relaxed lattice parameters. TEM studies directly prove that the irradiation leads to intermixing of Co with Pt layers what results in creation of substitutional Pt1xCox alloys (Fig. 1c). Such alloys exhibit a fcc structure with lattice parameter a decreasing with increasing of Co content.

Table 1 The structural parameters of as deposited Pt/Co/Pt/Al2O3 trilayers with different thickness of the Pt buffer. As deposited trilayer on Al2O3(0001)

Pt(3 nm)/Co(3 nm)/Pt(5 nm) Pt(3 nm)/Co(3 nm)/Pt(10 nm) Pt(3 nm)/Co(3 nm)/Pt(33 nm)

Hexagonal unit cell

Rhombohedral unit cell

aH (Å)

c (Å)

c/a

ar (Å)

a (°)

2.774(1) 2.772(1) 2.767(1)

6.818(3) 6.797(3) 6.782(3)

2.458 2.452 2.451

2.780(1) 2.774(1) 2.768(1)

59.85(5) 59.95(5) 59.97(5)

arelaxed of the cubic unit cell (Å)

Stress

3.927(1) 3.921(1) 3.914(1)

Compressive Compressive Relaxed

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E. Dynowska et al. / Nuclear Instruments and Methods in Physics Research B 364 (2015) 33–39

(a)

λ = 1.23984 A

100000

PtCo 111 d = 2.182 A

00.6 Al2O3

1E7

spot 06

Intensity (counts)

Intensity (counts)

1000000

Thickness fringes 10000

(b)

00.6 Al2O3

λ = 1.23984 Α

spot 08

PtCo 111 d = 2.185 A

1000000

100000

10000

1000 1000

100

100

20

24

28

32

36

40

20

22

24

26

28

(c)

1E7

Al2O3 00.6

λ = 1.23984 Α

spot 09

32

34

36

38

40

(d)

λ = 1.23984 Α

spot 10

1000000

1000000

Intensity (counts)

Intensity (counts)

1E7

30

2θ (deg)

2θ (deg)

100000

10000

PtCo 111 d = 2.250 A

1000

100000

10000

Pt 111 d = 2.267 A

1000

100

100 20

22

24

26

28

30

32

34

36

38

40

2θ (deg)

20

22

24

26

28

30

32

34

36

38

40

2θ (deg)

Fig. 5. The diffraction patterns of the irradiated Pt(3 nm)/Co(3 nm)/Pt(5 nm) trilayer performed with the use of micro-beam synchrotron radiation k = 1.23984 Å, (range of 1 1 1 Pt peak) for the spots with different number N of EUV pulses: (a) N = 1000 pulses, (b) N = 100 pulses, (c) N = 10 pulses, and (d) the diffraction pattern from not irradiated area.

The shapes of diffraction peaks measured for the spots with different number N of accumulated EUV pulses (Figs. 5a–c) vary from each other. For the highest irradiation dose (N = 1000) the intensity of the peak related to Pt1xCox alloy (d111 = 2.182 Å) is very strong whilst the intensity of the peak from the spot with N = 100 is much weaker. This suggests that the volume of the alloy created by irradiation in the spot with N = 100 (d111 = 2.185 Å) is smaller than that of spot with N = 1000. Because d111 value is slightly larger than that for spot with N = 1000 it can be deduced that content of cobalt in the Pt–Co alloy decreases. The shape of diffraction pattern obtained in the case of N = 10 irradiated with the lowest dose is very similar to that obtained in the non-irradiated place but they differ by d111 spacing which is slightly smaller in the with N = 10 (d111 = 2.250 Å and d111 = 2.267 Å for non-irradiated place). This indicates the existence of Pt–Co alloy with relatively low content of cobalt (Fig. 5c and d). In conclusion, while decreasing number of accumulated pulses, both the volume and contents of Co in Pt–Co alloys decrease. Unfortunately, we cannot determine the real composition of the alloys in individual spots because the measurements of the asymmetrical reflections and in consequence the relaxed lattice parameter of the alloys were not available. The X-ray diffraction measurements of the quasi-uniformly EUV irradiated sample with N = 30 pulses per spot have been performed at the laboratory diffractometer with the use of Cu Ka1 radiation k = 1.540598 Å. During measurements the whole surface of the

sample (5  5 mm2) has been exposed to X-rays. In a such measurements the obtained signal is averaged over the whole sample. The 2h-x diffraction patterns in the wide range of 2h angles covering symmetrical 1 1 1 and 2 2 2 as well as asymmetrical 1 1 3 reflections from the Pt layers and respective reflections 00.12 and 10.10 from the Al2O3 substrate have been obtained as well. A comparison these results with that from synchrotron micro-beam measurements obtained for separated spots in the vicinity of 1 1 1 Pt peak is shown in Fig. 6a. The shape of the pattern presented in the Fig. 6a is very similar to that obtained from spot with N = 1000 (Fig. 5a). Moreover, the lattice spacings d111 in both cases are the same: d111 = 2.182 Å. However, it does not mean that these results are identical because the composition of the Pt–Co alloy created in the spot with N = 1000 cannot be determined. For the quasi-uniformly irradiated sample the determination of the stress and relaxed lattice parameter (arelaxed) of the cubic Pt1xCox alloy have been done according to the procedure described in the previous paragraph. The value of the alloys lattice parameter arelaxed as well as the dependence of the lattice parameter on the Pt concentration for different Pt–Co alloys are needed for composition estimation. Such dependence is shown in Fig. 7 – the black squares are the experimental points taken from the work by Ferrer et al. [24], and line is the result of analytical fit to experimental data. The obtained curve is described by the equation:

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E. Dynowska et al. / Nuclear Instruments and Methods in Physics Research B 364 (2015) 33–39

(a)

Pt1-x Cox 100000

Intensity (counts)

111 d ~ 2.182 A

1000000

Intensity(counts)

(b)

00.6 Al2O3

λ = 1.540598 A

100000

10000

00.12 Al2O3

00.6 Al2O3

λ = 1.540598 Α 111 Pt0.9Co0.1

222 Pt0.9Co0.1

10000

1000

100

1000 10

25

30

35

40

45

20

50

30

40

50

2θ (deg)

60

70

80

90

100

2θ (deg)

Fig. 6. (a) The part of 2h-x diffraction pattern obtained from quasi uniformly irradiated Pt(3 nm)/Co(3 nm)/Pt(5 nm)/Al2O3 sample (b) 2h-x diffraction pattern in large range of 2h-angles of test sample of Pt0.9Co0.1(50 nm)/Al2O3(0001) alloy.

3.95

errors arising during measurements it was concluded that the precision of the x-value determination is ±0.02. The final results of structural studies obtained for irradiated samples as well as for the test alloy sample are collected in the Table 2.

Y =3.54811+0.0054 X-1.66641E-5 X2

Lattice parameter (A)

3.90 3.85 3.80 3.75

4. Conclusions

3.70 3.65 3.60 3.55 3.50 0

20

40

60

80

100

Concentration (at % Pt) Fig. 7. Dependence of the lattice parameter with the Pt concentration for different Pt–Co alloys. Analytical fit to the experimental points had been done on the basis of experimental data given in Ref. [24].

y ¼ 3:54811 þ 0:0054x  1:66641 E5 x2

ð4Þ

where x – concentration of Pt, y = arelaxed – proper to x-value. The composition of the Pt1xCox alloy with known arelaxed can be simply estimated on the base of above equation. In order to verify the measurement and calculation procedures used to determine the composition of this kind of alloys as well as the estimation of accuracy of obtained results the test sample of alloy Pt0.9Co0.1(50 nm)/Al2O3(00.1) obtained in co-deposition of Co and Pt was studied (Fig. 6b). After analysis of all experimental

The X-ray diffraction measurements have been performed with the use of micro-beam synchrotron radiation as well as the laboratory diffractometer. The stress and relaxed lattice parameters of the Pt films were determined on the base of measurements of the symmetrical and asymmetrical reflections, respectively. The methodology of these measurements and calculations has been developed and described in details. It was shown that thickness of the Pt-buffer layer affects the shape of diffraction pattern and calculated structural parameters. Pt(3 nm)/Co(3 nm)/Pt(5 nm) trilayers have been irradiated in different ways (isolated spots or quasi-uniform irradiated sample) with extreme ultraviolet light pulses. TEM studies show that the irradiation gives rise to intermixing of Co with Pt in the whole volume of trilayer. Irradiation of the samples resulted in severe changes of their diffraction patterns. Respective interpretation of the diffraction patterns confirmed creation of Pt1xCox alloys. The composition of the alloy has been estimated on the basis of the lattice parameter of relaxed unit cell of the alloy and using the dependence of the lattice parameter with the Pt concentration for different Pt–Co alloys reported in the literature. The correctness and precision of the composition determination have been proved by study of the test sample of Pt0.9Co0.1(50 nm)/Al2O3(00.1) alloy.

Table 2 The structural parameters of the irradiated Pt(3 nm)/Co(3 nm)/Pt(5 nm)/Al2O3(00.1) and test alloy Pt0.9Co0.1(50 nm)/Al2O3(00.1) samples. Pt(3 nm)/Co(3 nm)/Pt(5 nm)/Al2O3(00.1) Pt1xCox Local irradiation measured with the use of synchrotron micro-beam Pt1xCox Quasi-uniform irradiation measured at the laboratory diffractometer Pt0.9Co0.1 Nominal composition of the test sample

Spot

6 8 9

Hexagonal unit cell aH c (Å)

a\cubic in growth direction (Å)

arelaxed of the cubic unit cell (Å)

Composition of Pt1xCox x

Stress

–

3.779(1) 3.784(1) 3.897(1)

–

? ? ?

? ? ?

3.779(2)

3.792(2)

0.45(2)

tensile

3.881(2)

3.889(2)

0.13(2)

tensile

2.685(1) 6.552(3) c/a = 2.44 2.752(1) 6.723(3) c/a = 2.443

E. Dynowska et al. / Nuclear Instruments and Methods in Physics Research B 364 (2015) 33–39

Acknowledgements This work was partially supported by the Polish National Science Center (Grant No. 2012/06/M/ST3/00475). The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP712007-2013) under grant agreement n° 312284 (CALIPSO). References [1] Y.P. Lee, R. Gontarz, Y.V. Kudryavtsev, Phys. Rev. B 63 (2001) 144402. [2] J.-W. Lee, J. Kim, S.-K. Kim, J.-R. Jeong, S.-C. Shin, Phys. Rev. B 65 (2002) 144437. [3] O. Rader, E. Vescovo, J. Redinger, S. Blügel, C. Carbone, W. Eberhardt, W. Gudat, Phys. Rev. Lett. 72 (1994) 2247. [4] W.J. Antel Jr., M.M. Schwickert, T. Lin, W.L. O’Brien, G.R. Harp, Phys. Rev. B 60 (1999) 12933. [5] C.L. Canedy, X.W. Li, G. Xiao, Phys. Rev. B 62 (2000) 508. [6] B.N. Engel, C.D. England, R.A. Van Leeuwen, M.H. Wiedmann, C.M. Falco, Phys. Rev. Lett. 67 (1991) 1910. [7] O. Robach, C. Quiros, P. Steadman, K.F. Peters, E. Lundgren, J. Alvarez, H. Isern, S. Ferrer, Phys. Rev. B 65 (2002) 054423. [8] J.-W. Lee, J.-R. Jeong, S.-C. Shin, J. Kim, S.-K. Kim, Phys. Rev. B 66 (2002) 172409. [9] J.C.A. Huang, L.C. Wu, A.C. Hsu, Y.M. Hu, T.H. Wu, C.H. Lee, Phys. Rev. B 59 (1999) 1209. [10] S.-B. Choe, S.-C. Shin, Phys. Rev. Lett. 86 (2001) 532. [11] H. Brandle, D. Weller, J.C. Scott, S.S.P. Parkin, C.-J. Lin, IEEE Trans. Magn. 28 (1992) 2967.

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