Multilayered and alloyed Fe-Co and Fe-Ni nanowires physicochemical studies

Journal of Magnetism and Magnetic Materials 484 (2019) 67–73

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Research articles

Multilayered and alloyed Fe-Co and Fe-Ni nanowires physicochemical studies

T

⁎

B. Kalska-Szostkoa, , U. Klekotkaa, W. Olszewskib,c, D. Satułab a

Institute of Chemistry, Ciołkowskiego 1K, 15-245 Białystok, Poland Faculty of Physics, Ciołkowskiego 1L, 15-245 Białystok, Poland c ALBA Synchrotron Light Source, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallès, Barcelona, ES, Spain b

A R T I C LE I N FO

A B S T R A C T

Keywords: Magnetic materials Alloy nanowires Multilayered nanowires Electrochemical deposition Magnetic properties Mössbauer spectroscopy

Anomalous deposition of multi-element nanowires continuously interests scientists to study such a system. In this paper, two types of magnetic nanowires were electrodeposited: multilayered and alloy-like. Fe-Co and Fe-Ni nanowires with various relative molar ratio were prepared by DC electrodeposition in aluminum oxide matrix, with a mean pore diameter of 140 ± 20 nm. The nanostructures were investigated in two states: released and within the matrix, using the following techniques: Scanning Electron Microscopy, Energy Dispersive X-ray spectroscopy, X-ray diffraction, Infrared, and Mössbauer spectroscopy. The Scanning Electron Microscopy showed that the length of Fe-(Co, Ni) nanowires is of the order of 3 µm and the diameter determined by the pores of the anodic aluminum oxide templates. The X-ray diffraction and Mössbauer spectroscopy also showed that the fabrication method allows for the obtainment of both multilayered as well as alloyed nanowires with tunable magnetic properties which depend on both the elements’ relative ratio and its ordering. The magnetic texture observed by Mössbauer measurements demonstrated the almost random distribution of magnetic moments of iron in the studied samples which are rather unusual in layered systems.

1. Introduction Fabrication of multilayered and alloyed nanowires have attracted much attention because of their interesting properties that include: electron localization, perpendicular magnetic anisotropy, enhanced coercivity and giant magnetoresistance [1,2]. Likewise, Fe-Ni alloys are known for their extraordinary deviation of its saturation magnetization and magnetostriction [3]; therefore, it can be applied as thermostatic bimetals [4]. Preparation of such composition nanowires can enhance these properties and can be dependent on alloyed or multilayered morphology. A variety of nanomaterials can be obtained in many different ways: wet chemistry, organometallic reactions, ball milling, electrochemistry, sol-gel reactions, condensation, molecular beam epitaxy or sputtering, etc. [5]. In many cases, the properties of final materials depend on fabrication procedure, their crystal structure, size, surface modification, solution composition, etc. [6]. The extraordinary behavior of nanostructures can be explained by the fact that objects in the nanosize range have a different surface-to-volume ratio in comparison to bulky forms. The final critical value of the ratio depends on the shape, morphology, crystal structure and surface roughness [7,8]. To explain the extraordinary properties of many nanomaterials, their

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relationship with unsaturated bonds at the surface should be considered. This is due to the fact that strong modification of the surface electronic band structure and, thereby, chemical properties of the materials, which reflect in their reactivity, are expected [9]. Some modifications of the properties can be understood by introducing interfaces inside the objects, where wave functions of each layer must combine with each other in a specific way resulting in a unique energy state. Modifications of the electronic state of nano-objects can be accomplished by the presence of a layered internal structure or by polycrystallinity. In both cases, modifications of nanomaterials properties are expected, however, their nature can be totally different. Numerous studies have examined nanoparticles; although, we decided to consider elongated structures such as nanowires [10] to analyze the changes in observed properties as a consequence of modulated internal morphology and compare them. It is suggested by many scientists that the features of the electrochemically deposited objects, including their composition, is procedure dependent and the interplay between all parameters is still an urgent research issue [11]. One of the possibly least complicated wires fabrication method is electrodeposition [12]. Thermal decomposition of elements in the porous membranes (e.g. anodic aluminum oxide (AAO)) is also very

Corresponding author. E-mail address: [email protected] (B. Kalska-Szostko).

https://doi.org/10.1016/j.jmmm.2019.03.016 Received 28 June 2018; Received in revised form 31 January 2019; Accepted 4 March 2019 Available online 05 March 2019 0304-8853/ © 2019 Elsevier B.V. All rights reserved.

Journal of Magnetism and Magnetic Materials 484 (2019) 67–73

B. Kalska-Szostko, et al.

omitted in case of deposition with high aspect ratio [28,40,41]. The introduction of Co to the wires in some cases causes significant modification to the coercivity and remanence of the field ratio, which can be useful in wire applications [35]. In this paper, multilayered Fe/Co, Fe/Ni and alloy-like Fe-Co, as well as Fe-Ni nanowires produced by DC electrodeposition were examined. The difference/similarity of the Fe-Co and Fe-Ni systems have been discussed in respect of its chemical similarity. Importance of deposit composition as well as its internal structure is refined. The following molar ratios of the nanowires used were: 1:1, 2:1 or 2:2 for multilayered, and 1:0.25, 1:0.5, 1:0.75, 1:1 for alloy-like, to achieve access to variable composition, what reflects in wires properties. Physicochemical characterization was performed by scanning electron microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), infrared spectroscopy (IR) and Mössbauer spectroscopy (MS).

powerful [13–17]. Wires can also be obtained by deposition of elements in particular conditions on flat surfaces which were pre-structured by lithography, self-lithography, pre-deposition, oxidation, etc. This, however, often employs very sophisticated experimental setups [18]. In general, for many materials both alternating current (AC) and direct current (DC) deposition methods are effective. However, the quality of the wires changes with respect to deposition solution content, time and current conditions [19]. The detailed deposition mechanism, especially most interesting from the technological point of view, of Fe-Ni system is continuously not clear nor sufficiently understood and is still under debate [20–23]. It is mainly due to the presence of a strong anomalous co-deposition phenomenon which governs most cases and needs to be explained by general rules which is not a case and continuous research is performed on this subject [22,24–28]. Electrodeposition is often the most favorable option, especially when specific deposition circumstances allow scientists to fabricate unique materials. Electrodeposition of nanowires in AAO matrixes is, therefore, a very interesting, easy, and cheap alternative method of nanowires fabrication [29]. Optimization of the method and assignation of solution constituents role is especially required from the industrial point of view. Likewise, electrochemical deposition is an attractive method because of its effectiveness. There is a huge variety of possible ions that can be reduced in a reasonable time frame with almost no limitation in the sample shape and size. Recently, many metallic nanowires have been produced on AAO templates, including low and high melting points for pure metals such as Au, Ag, Zn and Ni, Fe, Co and their alloys, respectively [11,30,31] Ferromagnetic nanowires are rather commonly fabricated in AAO using both AC and DC deposition methods [32,33]. However, it is important to consider whether deposition conditions can influence the quality and length of obtained nanowires [34–37]. For instance, the wires obtained from Co via a DC deposition method can be well distributed and standing perpendicularly to the surface plane or be disordered and relaxed on the surface in respect of deposition time and ions concentration. Their magnetic properties (as ordered arrays) were found to be strongly related to the dimension and spatial arrangements (relative lengths, diameters, nanowires-to-nanowires separation, and periodicity) [34]. The AC method, in most cases, (for a sufficiently long time of deposition) ends up with wires which are more randomly oriented at the surface due to the strong magnetic interaction between each other, especially in the case of Ni, Co, and Fe. FeNi alloys are known as low coercivity materials. Deposition of bimetallic layers (eg. FeNi, FeCo) have some difficulties which are connected with the anomalous co-deposition of constituent elements. This means that the less noble metal is deposited preferentially in respect to its counterpart [38,39]. This phenomenon is of crucial importance since various FeNi alloys have diverse properties which are caused by variable composition and their structure. These facts should be considered in the analysis of alloyed and multilayered nanowires. However, also kinetic contributions and hydrogen evolutions related phenomena cannot be

2. Experimental 2.1. Material and apparatus To obtain multilayered and alloy nanowires, the following chemicals which originate from POCH were used: FeSO4·7H2O, CoSO4·7H2O, NiSO4·7H2O, H3BO3, ascorbic acid, NaOH, and acetone. The quality and composition of the nanowires were investigated by scanning electron microscope (model: Inspect 2000) with acceleration voltage 15 kV, equipped with EDX detector. The analysis of the crystal structure was performed using X-ray diffractometer Agilent Technologies SuperNova equipped with a Mo microfocused source (Kα2 = 0.713067 Å). The FT-IR spectra were collected in reflection mode at room temperature (RT) by Nicolet 6700 Infrared spectrometer working in the spectral range between 500 and 4000 cm−1. Mössbauer spectra were measured using the spectrometer working in a constant acceleration mode with a 57CoCr radioactive source.

2.2. Anodic aluminum oxide matrix All types of nanowires were fabricated in AAO matrix obtained in an elaborated 3-step anodization procedure in H3PO4 solution resulting in a pore size of about 140 ± 20 nm. Pre-studies of pores quality, dimension and anodization condition were subject of other papers [10]. During the anodization process, the area exposed to the procedure was kept the same in order to avoid any discrepancy caused by differences in current density flow. Pores surface coverage in average quality AAO used was about 46–52%. Therefore, average pores distance is of 40–50 nm. The example image of AAO matrix before the electrodeposition process is presented in Fig. 1A.

Fig. 1. SEM images of (A) AAO matrix before the electrodeposition process; (B) Fe-Co alloy nanowires; (C) Fe-Ni alloy nanowires and (D) Fe/Co layered nanowires released from the matrix. 68

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DC method for 20 min, with the current value of 10 mA (10 × 15 mm2). The summary of the wires resultant type is presented in Table 1. In addition, in the case of alloy-like nanowires role of the solution, constituents were checked by removing C6H8O6 or H3BO3 form the solution.

Table 1 Summary of the nanowires composition. In column: (1) deposition time ratio (1 stand for 1 min, 2 – for 2 min), (2) a total number of layers (Fe, Co or Ni) in layered wires summarized to total deposition time, (3) – molar ratio in alloyed wires. Deposition time ratio (FeSO4:MeSO4) (1) Layered Series name

Number of layers (2)

1:1 2:2 2:1

10:10 5:5 7:6

Molar ratio (FeSO4:MeSO4)

3. Results and discussion

(3) Alloy Series name

Fe:Me

3.1. SEM studies

1:0.25 1:0.5 1:0.75 1:1

The surface of AAO matrixes and morphology of deposited Fe-Co (/Co) or Fe-Ni nanowires was imaged by SEM, the wires were released from the template and placed on the conducting carbon tape. The obtained pictures of the selected samples are presented in Fig. 1 (B-D). Fig. 1 A shows the AAO matrix before the electrodeposition process. As one can see, the arrangement of the pores is rather irregular. Fig. 1 B-D presents the obtained Fe-(Co, Ni) nanowires. These images confirm the successful deposition of nanowires in the proposed matrixes. The form of the wires is very dense, but some voids are also present, what can influence an inhomogeneous magnetic interaction between wires, but its density is very low (1–2%). Therefore, the total percentage of uneven structures is small and samples can be considered homogenous. The released nanowires are continuous with a length of approximately 3 μm, which is determined by the templates depth (Fig. 1 D). The diameter of the wires is also in agreement with the matrix fabrication procedure.

2.3. Preparation of multilayered nanowires In our study, two series of multilayered nanowires were prepared. The first one was composed of Fe and Co, and the second one was composed of Fe and Ni elements. The nanowires were electrodeposited on templates (10 × 15 mm2 in size) from the following solutions: FeSO4·7H2O, CoSO4·7H2O (or NiSO4·7H2O), H3BO3 and ascorbic acid (C6H8O6) in a molar ratio (0.12:0.12:0.48:0.02), respectively. The electrodeposition process was conducted for 20 min (in total) in DC mode, with the current value 10 mA. in the AAO matrix, nanowires were released from the temple by dissolving it in 1 M NaOH. Then, nanowires were washed with distilled water and acetone to remove ethanol and other residues. As a consequence, 3 various types of Fe/Co and Fe/Ni nanowires were obtained. In all cases, molar ratios of Fe/(Co or Ni) were 1:1, 2:2 and 2:1. Multilayered nanowires were fabricated by sequencing deposition of Fe and Co or Ni species. The template was each time replaced to one or another selected solution. In one series of the nanowires, the sequence deposition duration for either element was 1 min, in the other series it was 2 min, and in the third case AAO matrix, was kept for 2 min in Fe2+ and 1 min in Co2+ or Ni2+ solution. In Table 1, fabricated multilayered nanowires are summarized.

3.2. EDX studies The selected layered and alloy type nanowires were examined by EDX. The obtained spectra are presented in Fig. 2. In Table 2 the results of the elemental analysis of the tested wires are reported. The elemental analysis of the structures was carried out by EDX spectrometer combined with SEM microscope. All wires show expected elements present. Aside from this, the ratios obtained between the deposited elements were very close to the expected in case of layered systems and suggest not disturbed process. Therefore, SEM images together with EDX elemental analysis confirm co-deposition of the proposed elements in the wires regardless of the composition (Co or Ni). The difference in resultant objects between Co- and Ni-Fe alloys is evident in alloyed case. That is connected to the nature of anomalous deposition phenomena what reflects in more preferred presence of Fe in deposit over Co or especially Ni [42–44]. Difference between Fe-Co and Fe-Ni series can be followed in Table 2.

2.4. Preparation of alloy-like nanowires To fabricate alloy-like nanowires, the same conditions during the deposition were used. Here, the process was performed in one pot solution which contains adequate ions (Fe2+ and Co2+ or Ni2+) in various molar ratios. The electrodeposition process was conducted by the

Fig. 2. EDX spectra of some layered (A-B) and alloy-like nanowires (C-D). 69

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Table 2 The elemental analysis from EDX spectrometry for the selected layered and alloy-like nanowires. Element

Weight (%) (1:0.75)

Sample (1:0.75)

(1:0.5)

(1:0.5)

alloyed Fe Co Ni

Table 3 Lattice parameters calculated from X-ray diffractograms, together with literature value BCC Fe, FCC Co, and FCC Ni.

51 ± 3 49 ± 3

(2:2)

(1:1)

layered 76 ± 4 24 ± 2

58 ± 3 42 ± 3

81 ± 4 19 ± 4

50 ± 3 50 ± 5

Fe

43 ± 2

a [Å]

%BCC

a [Å]

% FCC

Fe

literature experimental

1 1

2.87 [49] 2.87

– –

– –

– –

Fe-Co

literature Co layered

– 1:1 2:2 2:1 1:0.25 1:0.5 1:0.75 1:1

– 2.86 2.85 2.86 2.87 2.86 2.85 2.85

– 95 90 96 100 100 100 100

3.53 [50] 3.50 3.52 3.51 – – – –

% Co 5 9 4

– 1:1 2:2 2:1 1:0.25 1:0.5 1:0.75 1:1

– 2.87 2.86 2.85 2.87 2.87 2.86 2.86

– 43 48 86 100 100 100 100

3.58 [51] 3.52 3.53 3.53 – – – –

% Ni 57 52 14

57 ± 4

alloyed

3.3. X-ray diffraction To check for a crystal structure among the studied nanowires, XRD measurements were performed. X-ray diffraction allowed for the examination of modification in nanowires structure in respect to the composition and/or morphology. For XRD measurements, a small amount of extracted wires were glued via highly viscous oil to nylon loop and placed in the center of the goniometer. The obtained results are shown in series in Fig. 3. On diffractograms most important peaks via Muller hkl indexes were marked. In Fig. 3 (A) diffractograms present a set of the multilayered nanowires Fe/Co with the deposition time 1:1, 2:2, and 2:1 together with reference Fe wires, in (B) respective Fe/Ni nanowires, and in (C) alloyed nanowires for Fe-Co and Fe-Ni for molar ratio 1:0.5 and 1:1. In every spectrum, hkl indexes typical for bcc Fe are observed (1 1 0) (2 0 0) (2 1 1) (2 2 0) (3 1 0) [45] which meant that stabilization of that structure has been achieved [46]. In the spectra of multilayered Fe/Ni, additional diffraction peaks with hkl indexes typical for Ni metal in FCC phase can be marked (1 1 1) (2 0 0) (2 2 0) (3 1 1) [47]. Selected (1 0 0) (0 0 2) and (1 0 1) signals observed in multilayered Fe/Co samples can be identified via hkl Müller indexes as HCP Co phase [48] together with FCC one (1 1 1) (2 0 0) (2 2 0) (3 1 1). It can be concluded that for 2:1 Fe to Co elements ratio only FCC phase is seen, while for 2:2 either FCC and HCP Co is measured. This observation is in agreement with the scenario that thicker Co layer in case (2:2) was obtained. In panel (C) alloyed wires diffractograms of both systems are depicted. Here only patterns typical for BCC phase are seen which means that designed alloy with Fe crystal structure was obtained. Summarizing the X-ray diffraction measurements, one can conclude that in the case of Fe/Ni multilayered samples, both BCC and FCC crystal structures are present which is expected for growth regimes and segregation of the elements is evident. On the other hand, for Fe/Co typical reflections for BCC and

Me

Fe-Ni

literature Ni layered

alloyed

FCC and HCP are assigned. Such results strongly suggest that the studied nanowires indeed have an internal layered layout. The alloyed nanowires show reflections typical for BCC crystal structure, which suggests that the species are mixed with expected Fe-(Co, Ni) concentration depending on elements molar ratio used (see EDX experiments). These conclusions were also confirmed by Mössbauer measurements described in Section 3.4. Numerical analysis of the diffractograms allow for the calculation of cell parameters of resultant structures and it also confirms the tendency that increasing amount of Co or Ni decreases the cell constant value (see Table 3). Estimation of elements content based on XRD data analysis is in agreement with EDX experiments. However, one should remember that values must be compared with some proportionality, which takes into account differences in cell symmetry. 3.4. IR spectroscopy Released nanowires were also tested by IR spectroscopy to observe any modifications taking place on the surface based on the wires composition and solution related species. Representative spectra are collected in Fig. 4.

Fig. 3. X-ray diffraction patterns of (A, B) multilayered nanowires, (C) alloyed nanowires. 70

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Fig. 4. IR spectra of Fe-Ni alloyed type with respect to molar ratio;

In Fig. 4 IR spectra of Fe-Ni nanowires with a type of alloy are presented. In almost every spectrum, small signals typical for Fe-O bonds in maghemite (681–643 cm−1) [52], goethite (824–840 cm−1) [53] and lepidocrocite (1058–1090 cm−1) [52] can be observed. Bands in the spectra ranging between 1100 and 2950 cm−1 can be observed due to residuals adsorbed from other products used in the solution (mostly from ascorbic acid). A wide band at around 3300–3310 cm−1 is connected with the presence of O–H bonds mainly in water. The presented results suggest a surface oxidation process of Ni and Fe layers which can occur after release from the matrix [52,54]. Ni-O vibrational band lies below the detection limits of our system [55]. Protection from oxidation should be tested in further studies.

3.5. Mössbauer spectroscopy The Mössbauer spectra of alloyed and layered nanowires of Fe-Co (/Co) and Fe-Ni (/Ni) being in templates were measured at RT. Measured spectra are presented in Fig. 5 A. Moreover, in order to study the influence of solution composition on the magnetic properties, the Mössbauer measurements of alloyed Fe-Co and Fe-Ni nanowires with molar ratio 1:1 were performed and spectra are presented in Fig. 5 B. In order to describe the shapes of the spectra, two components, one sextet, and one doublet, were used. In the analysis, the broadening of the lines of the sextet of Gaussian magnetic hyperfine field (m.h.f.) distribution characterized by standard deviation σB was assumed. The width of the Lorentzian lines of the sextet was taken from the calibration spectra and fixed, while for the doublet, there was a free parameter in the fitting procedure. The solid lines in Fig. 5. represent the best fit. The numerical results of hyperfine fields of the sextet for all samples are presented in Table 4. The quadrupole splitting of the sextet was fixed and assumed to be zero. The analysis shows that hyperfine field parameters of the doublet, isomer shift (IS) and quadrupole splitting (QS) were the same within the error bars for all samples and equal IS = (0.20 ± 0.03) mm/s and QS = (0.33 ± 0.06) mm/s, respectively. The relative intensity of the doublet varies between 20% and 40% for the measured samples. Discussion of the doublet origin was performed before and it was concluded as a spontaneous surface or grain boundary oxidation due to no epitaxial growth and not oxygen-free conditions [56]. Such an effect of the oxidation process is difficult to control during sample preparation. In addition, the presence of interfaces in layered nanowires can contribute to the spectra as a doublet. The significance of interfaces was discussed in the case of multilayered samples on various systems [57–60]. The m.h.f. observed for layered Fe/Co and Fe/Ni samples were very close to 33 T, which agreed with the m.h.f. observed for pure BCC iron at room temperature [61]. In the alloy-like samples the values of m.h.f.

Fig. 5. Mössbauer spectra of the alloyed and multilayered, Fe-Co and Fe-Ni nanowires. The solid red lines represent the best fits, green and blue one respective subspectra, (A) wires composition dependence, (B) solution composition dependence. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

are higher than 33 T. In the samples, Fe-Co is slightly above 34.5 T, and for Fe-Ni around 34 T [59,60]. These values were consistent with the results from bulk Fe-Co and Fe-Ni disordered alloys presented in Ref. [62]. Such results confirm that higher atomic intermixing appears in the case of alloy deposition compared to the layered one. Moreover, such observation is confirmed by the results of the line width obtained both for Fe-Co and Fe-Ni samples. The broadening sextet line width of multilayered samples are smaller compared to alloyed samples. Such an 71

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4. Conclusion

Table 4 Hyperfine parameters for both layered and alloy-like nanowires. m.h.f - magnetic hyperfine field [T], σB – standard deviation of Gaussian magnetic hy→ ) 2〉 γ ·m perfine field distribution [T], IS – isomer shift [mm/s], 〈 (→ – magnetic Fe texture (description in the text below). sample

m.h.f ± 0.5 T

σB ± 0.05

IS ± 0.05

→ )2 〉 〈 (→ γ ·m ± 0.1 Fe

Fe/Co

layered

1:1 2:2 2:1

32.9 33.0 33.0

0.36 0.33 0.31

0.01 0.01 −0.01

0.3 0.4 0.4

Fe-Co

alloyed

1:0.25 1:0.5 1:0.75 1:1

36.1 35.5 35.4 34.6

1.25 1.38 1.45 1.64

0.04 0.04 0.01 0.04

0.5 0.5 0.4 0.2

Fe/Ni

layered

1:1 2:2 2:1

33.7 33.0 33.1

0.60 0.90 0.92

0.01 0.02 0.02

0.5 0.5 0.4

Fe-Ni

alloyed

1:0.25 1:0.5 1:0.75 1:1

33.7 34.0 34.0 34.0

0.93 1.08 1.17 1.19

0.02 0.03 0.02 0.04

0.5 0.5 0.5 0.5

Fe-Co

standard no H3BO3 no C6H8O6

1:1

35.0 34.6 35.0

1.64 1.27 1.27

0.04 0.04 0.03

0.2 0.5 0.3

Fe-Ni

standard no H3BO3 no C6H8O6

1:1

34.0 34.0 34.0

1.20 1.19 1.17

0.04 0.02 0.03

0.5 0.5 0.5

Fe-Co and Fe-Ni are alloys which continuously attract scientist to study their properties in different forms and fabrication conditions. Anomalous deposition strongly depends on the process starting condition: surface quality, solution composition, active species concentration, and time. Therefore, analysis of particular nanowire systems is worth studying in order to understand the relationship between the external parameters and internal morphology of the wires. The following conclusions can be achieved from the qualitative analysis:

effect is clearly visible for Fe-Co samples and less for Fe-Ni. All the above observations and XRD results show that using our sample preparation method, one can obtain a good quality of both multilayered or alloyed nanowires. The Mössbauer spectroscopy helped determine the magnetic texture of Fe magnetic moments in the sample from the transition probabilities. The lines intensities in the sextet satisfy the following relation:

1) The DC electrodeposition method allows for the obtainment of both alloyed and multilayered nanowires in anodic aluminum oxide matrix pores with good efficiency. 2) The average lengths of the obtained nanowires are about 3 µm and the diameters are governed by the diameter of the pores of the anodic aluminum oxide matrix. 3) It is difficult to avoid spontaneous surface oxidation during the wires-releasing process or grain boundary oxidation during the electrodeposition process; however, this can be avoided by using a less oxide environment during deposition and wires treatment. 4) The magnetic moments of Fe show the almost random distribution with a small tendency to the arrangement along the nanowires’ main axis, which is caused by diameter to long axis ratio. 5) Subsequent layer-by-layer growth allows for the obtainment of Co FCC crystal structure for thin layers, while hcp is observed for the thicker film. 6) During alloy-like deposition, Fe BCC symmetry is preserved in studied composition range. Anomalous deposition is more pronounced for Fe-Ni case. 7) Presented results are consistent with the foreseen growing scenario (mixed or layered). 8) Solution composition influences wires growth especially in case of Fe-Co system. Here relative magnetic moments orientation depends on the electrolyte additives.

I1: I2: I3: I4 : I5: I6 = 3: z: 1: 1: z: 3

Acknowledgments

Where z value helps estimate the average square of the cosine of the γ ) and the direction of angle between the direction of the gamma ray (→ → the magnetic hyperfine field (mFe )

Mössbauer spectroscopy was performed in close collaboration with the Department of Physics at the University of Bialystok. The work was partially financed by EU funds via the projects with contract numbers POPW.01.03.00-20.034/09-00 and POPW.01.03.00-20-004/11, COST MP 1408 and by NCN funds, projects numbers UMO-2014/13/N/ST5/ 00568.

→ )2 = 4 − z (→ γ ·m Fe 4+z where brackets < > denote an average over the magnetic hyperfine → ) γ ) and (m field orientation in the samples, and (→ Fe are unit vectors of gamma beam direction and magnetic hyperfine field, respectively [63,64]. In the case of random distribution of magnetic hyperfine field, → )2 is equal to 0.33(3). In the case of a parallel and perpendicular (→ γ ·m Fe arrangement of m.h.f. in respect of gamma direction, this value equals 1.0 and 0.0, respectively. → )2 indicate the almost random disγ ·m The obtained values of (→ Fe tribution of magnetic hyperfine field distribution with a small tendency to the arrangement perpendicular to the sample plane (along with the wires long axis) can be seen in Table 1. Only for one sample, Fe-Co alloyed sample with 1:1 M ratio, did the results show the arrangement in the plane of the sample (perpendicular to wires long axis). Such behavior is difficult to understand and should be further studied. In the case of solution dependences of magnetic moment arrangement, one can observe that for Fe-Ni nanowires, there is no influence of the solution composition on magnetic moments arrangement. However, for Fe-Co nanowires, the magnetic moments have a tendency to the perpendicular direction with respect to gamma beam direction when the solution is without H3BO3.

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