Assessment of Layer Thickness and Interface Quality in CoP

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Assessment of Layer Thickness and Interface Quality in CoP Electrodeposited Multilayers Irene Lucas, David Ciudad, Manuel Plaza, Sandra Ruiz-Gómez, Claudio Aroca, and Lucas Perez ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b02577 • Publication Date (Web): 06 Jul 2016 Downloaded from http://pubs.acs.org on July 7, 2016

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ACS Applied Materials & Interfaces

Assessment of layer thickness and interface quality in CoP electrodeposited multilayers Irene Lucas,∗,†,k David Ciudad,‡ Manuel Plaza,¶ Sandra Ruiz-Gómez,§ Claudio Aroca,‡ and Lucas Pérez§ †Dpto. F´ısica de la Materia Condensada, Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain ‡Instituto de Sistemas Optoelectrónicos y Microtecnolog´ıa. Universidad Politécnica de Madrid. 28040 Madrid (Spain) ¶Dept. Fisica de la Materia Condensada, Universidad Autónoma de Madrid §Dept. F´ısica de Materiales. Universidad Complutense de Madrid. 28040 Madrid (Spain) kInstituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, Mariano Esquillor, Edificio I+D, 50018 Zaragoza, Spain E-mail: [email protected]

Abstract The magnetic properties of CoP electrodeposited alloys can be easily controlled by layering the alloys and modulating the P content of the different layers by using pulse plating in the electrodeposition process. However, due to its amorphous nature, the study of the interface quality, which is a limitation for the optimization of the soft magnetic properties of these alloys, becomes a complex task. In this work we use Rutherford Backscattering Spectroscopy (RBS) to determine that electrodeposited Co0.74 P0.26 /Co0.83 P0.17 amorphous multilayers with layers down to 20 nm-thick are composed by well-defined layers with interfacial roughness 1 ACS Paragon Plus Environment


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below 3 nm. We have also determined, using magnetostriction measurements, that 4 nm is the lower limitation for the layer thickness. Below this thickness, the layers are mixed and the magnetic behavior of the multilayered films are similar to the ones shown by single layers, thus going from in-plane to out-of-plane magnetic anisotropy. Therefore, these results establish the range in which the magnetic properties of these alloys can be controlled by layering.

Keywords electrodeposition; CoP; RBS; amorphous multilayers; magnetostriction

Introduction Soft amorphous alloys are a key element in many inductive magnetic devices. In particular, they are an essential element in fluxgate sensors in which an adequate selection and treatment of the core ensures the best performance of the device. 1,2 In fact, recent developed fluxgates are substituting SQUID (Superconducting QUantum Interference Device) magnetometers in medical applications, because they provides similar sensitivity and portability without the need of cryogenics. 3 Moreover, integrated microfluxgates are gaining attention in ”in-vitro” applications lately. 4,5 In this sense, CoP electrodeposited amorphous alloys has been proved to be very suitable materials for the integration in planar fluxgates. 6 The main advantage of the fabrication process of this material is the possibility of electroplating very thick soft ferromagnetic films — up to several tens of microns 7–9 — using a versatile and low cost deposition system where CoP is electrodeposited in multilayer form (Cox P1-x /Coy P1-y ). Single CoP layers, with thickness above 400 nm show a relatively strong perpendicular-to-surface anisotropy. 10 However, taking into account that the magnetic properties of the CoP alloys strongly depends on the P content, 11 the modulation of the P content in the perpendicular-to-surface direction 2 ACS Paragon Plus Environment

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produced in the multilayered samples allows controlling the magnetic anisotropy by varying the thickness and the composition of the different layers. 12–15 Although this modulation also produces an increase of coercivity due to pinning of the domain walls at the interfaces, coervicity remains below 10 A/m, 16 showing in-plane anisotropy and high permeability. This control of magnetic anisotropy and softening of the magnetic properties in multilayers is compulsory to use CoP amorphous alloys as magnetic core of miniaturized sensors and devices. 6 However, when reducing the layer thickness below a certain value, it is expected that roughness, diffusion effects, in-homogeneities during deposition, etc, could mix the different layers, affecting the sensing properties of the device. The study of the quality of the interlayer and layer thickness are therefore essential in order to understand the magnetic behavior of these multilayers. In addition, the limitation in the layer thickness for the control of these CoP layers have not yet been reported. In crystalline materials, the layering quality can be studied mainly by techniques based of X-ray diffraction or high resolution electron microscopy. These techniques allow for example, to study the interface quality of electrodeposited crystalline multilayers. 17,18 In the case of amorphous materials, these techniques are not the best option due to the lack of crystalline order. Therefore, exploring the use of new different techniques becomes interesting for the study of interfacial roughness and layer thickness of Cox P1-x /Coy P1-y multilayers, techniques which would be also useful for the study of other amorphous materials. In this work we combine Rutherford Backscattering Spectroscopy (RBS) with magnetostriction measurements to study the thickness and interface quality of amorphous multilayers. In the case of RBS, experimental results have been compared with simulations. To study thicknesses below the experimental limit of this technique, we have estimated the thickness and interface quality from magnetostriction measurements.

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Experimental Co0.74 P0.26 /Co0.83 P0.17 multilayers were fabricated by current-controlled electrodeposition on polycrystalline Cu substrates in a conventional two electrode cell using Co as counter electrode. The composition of the electrolyte used in the plating process was the following: CoCO3 (0.33 M), CoCl3 (0.76 M), H3 PO3 (0.76 M) and H3 PO4 (0.51 M). The electrolyte was kept at 80◦ C during electrodeposition. The composition of the layers can be continuously varied by changing the current density, as reported in a previous work. 14 The P content in the layers increases when the density current decreases. However, it is important to note that the composition of the layers also depends on the configuration of the electrochemical cell (geometry, stirring, etc). So, it is important to calibrate the composition for a particular set-up. In our case we have grown multilayers, pulsing the density current between −100 mA/cm2 and −500 mA/cm2 , corresponding to a composition of Co0.74 P0.26 and Co0.83 P0.17 respectively, measured by energy dispersive X-ray microanalysis (EDX). A potentiostat/galvanostat Metrohm Autolab PGSTAT303 in High Speed mode was used to control the growth. Figure 1 shows the evolution of current density and electrode potential measured during the growth of a multilayered sample. It can be seen that both, current and potential, have a sharp transition when pulsing the density current. More details about the electrolyte and growth conditions can be found in reference 14 and references therein. The thickness of the layers (t) were settled by the electrodeposition time, and has been modified together with the total number of layers N in order to keep constant the total thickness of the samples in 10 µm. We have grown multilayered samples with layers ranging from t=1 nm up to t=5 µm (N =10000 to N =2). X-ray diffraction experiments does not show any diffraction peak in any sample, meaning that all samples are amorphous. We have measured all the samples in a LakeShore Vibrating Sample Magnetometer system, finding that they are all ferromagnetic with the same saturation magnetization (µ0 MS ∼ 0.60 ± 0.04 T) and the same magnetic properties than those reported in previous works. 14,16 Rutherford backscattering spectroscopy (RBS) is an Ion Beam Analytical technique used 4 ACS Paragon Plus Environment

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Figure 1: Evolution of current density and electrode potential with time measured during the growth of Co0.74 P0.26 / Co0.83 P0.17 multilayers. in materials science for the determination of the composition and structure. It is based on the measure of a backscattered beam of high energy ions impinging on a sample and can be particularly useful for the analysis of multilayered films. 19,20 RBS experiments were performed in a 5 MV terminal voltage Tandetron accelerator at the Centro de Micro-Análisis de Materiales (CMAM) in Madrid, using 4 He+ as incident ions. The ion beam was accelerated at 2 MeV. Unless otherwise stated, the experiments were done in normal incidence, with an exit angle of 9.50◦ and a scattering angle of 170.50◦ , both measured with respect to the incident beam. The resolution of the used detector was 20 keV. Experimental results have been fitted using SIMNRA 21 Version 6.04. In order to calculate the penetration depth we have used SRIM 2008 software. 22 When a magnetic material undergoes a change in magnetization along a particular direction, there is a fraction change of length along this particular direction. This effect is proportional to M2 and it is called linear magnetostriction, or simply magnetostriction (λ). The sign may be positive or negative and normally does not exceed 1%. Magnetostriction effect has been largely used in the development of magnetic sensors and devices, 23,24 as well as in Microelectromechanical systems. 25 However, considering the close relationship between magnetostriction and magnetization processes, it can be also used as a tool to have a 5 ACS Paragon Plus Environment


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deep insight in the magnetic properties of magnetic materials. In this sense we have carried out magnetostriction measurements in a homemade experimental set-up based on the optical method presented by Tam and Schroeder. 26,27 This system has been previously used for measuring magnetostriction in crystalline 28 and amorphous 29 materials as well as in amorphous CoP multilayers 15 similar to the one reported in this work. For measuring, the magnetic material is deposited on a non-magnetic substrate which is clamped by one end forming a cantilever. When a magnetic field is applied, the magnetic material changes its length but not the substrate, producing the bending of the cantilever. This bending is measured by the deflexion of a laser beam focused in one end of the cantilever. The bending can be correlated to the magnetostriction and the Young modulus. If we denote the relative change of length when applying a saturating magnetic field along the length of the cantilever as λHL and the change when applying a in-plane saturating magnetic field along the transversal direction as λHT , we can calculate the magnetostrictive constant as:

λS = 2(λHL − λHT )/3

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Results and discussion The interlayer quality of the CoP thin films has been studied by RBS. Penetration depths at 2 MeV, calculated using SRIM, are 3.42 µm for Co0.74 P0.26 and 3.30 µm for Co0.83 P0.17 . Both values are very similar because the atomic densities are practically the same for both compositions. From these values of the penetration depth and taking into account that the total thickness of the samples is 10 µm, it can be ensured that no RBS signal is coming from the substrate. Figure 2 shows several RBS spectra obtained in a CoP multilayers (solid line and dots) together with the fitting of the experimental data (solid lines) using SIMNRA software. Figure 2(a) corresponds to a multilayer composed by 100 layers, having each layer a thickness


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of 100 nm (N =100). The wave shape of the spectrum is due to the modulation of the composition in the sample. The contribution coming from each element to the total RBS signal has been calculated and it is also shown in the figure. The differences between experimental data and fitting below the channel 100 are due to the limitations in the number of the layers the program can simulate. The fitting with SIMNRA allows estimating the composition of each layer, finding the same values than the one measured with EDX within the experimental error (∼1%). The fitting also allows extracting information about the thickness of the different layers comprised in the penetration depth of the incident beam. In this case, the dispersion in the values of the thickness of each layer, goes from 4% (for N =100) to 7% (for N =500). 13000

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Figure 2: RBS experimental data and fitting for CoP multilayers formed by layers of (a) 100 nm, (b) 60 nm and (c) 20 nm. The calculated contribution of the different elements (Co, P and O) to the total RBS signal is also shown. Inset: zoomed part of the graph to better appreciate the fitting of the experimental data. Experimental results for multilayers with layers down to 60 nm can be perfectly fitted assuming the samples made by sticking Co0.74 P0.26 /Co0.83 P0.17 bilayers with the same thickness, within the 4-6% error mentioned before (see Figure 2(b)). Below this thickness, the signal to noise ratio is too low to extract useful information from the RBS spectra. By rotating the sample 60◦ the apparent thickness of the layer for the ion beam increases, making possible to study samples with layers down to 20 nm. Figure 2(c) shows the RBS spectrum measured in a multilayer with 20 nm-thick layers measured under these conditions, together



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with the fitting. Below this thickness, no information can be extracted from RBS. Although the experimental data can be fitted considering only CoP layers, the fitting improves when assuming the existence of a first oxidized layer of 10 nm in all samples. The presence of an oxidized layer can be noticed by the presence of an O peak in RBS spectra. From the inset of Figure 2(a) it is clear that both curves, experimental data and fitting using a model with oxidized layer, are in very good agreement even at the higher energies. Even though the samples could be surface oxidized due to natural oxidation, oxygen was not detected in the EDX measurements carried out before the RBS characterization. Therefore, the most plausible explanation as the source of this oxidized layer is the heating produced by the ion beam during RBS measurements. The interface roughness of the layers forming the multilayer, i.e. the layer thickness undulation, can also be estimated by a refinement of the fittings, being approximately 23 nm. The values for the multilayers are in between the roughness measured in samples constituted only by a single 10 µm layer, which is 2 nm for Co0.83 P0.17 and 3 nm for Co0.74 P0.26 respectively. In the case of a single layer sample, we have considered that the interface roughness obtained using SIMNRA coincides with the surface roughness. Taking into account that 20 nm is the smallest layer thickness we have been able to measure by RBS, the models implemented in SIMNRA are appropriate for the samples under study since the calculated roughness (2-3 nm) is much smaller than the thickness of the layers. As mentioned before, in a previous work 15 using magnetostriction measurements we show that the easy axis of magnetization for these CoP multilayered thick samples can be moved from perpendicular to in-plane when layering down to 10 nm. The RBS measurements reported in this work show that, at least down to 20 nm, the multilayers are composed by well-defined layers and this structure can explain the previously reported magnetic behavior. However, considering that the interface roughness of each layer forming the multilayer is below 3 nm, it should be possible to grow CoP multilayers with layers down to this value without considerable mixing of adjacent layers and thus, keeping unaltered the control of the magnetic properties


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of the multilayered structure. Unfortunately, RBS spectroscopy is not sensitive enough to characterize the thickness of the layers below 20 nm. RBS has also allowed us to check the growth rate of the electrodeposited CoP alloys which is 80 nm/s for a current density of −100 mA/cm2 and 8 nm/s for a current density of −500 mA/cm2 . Taking into account the strong dependence of the orientation of the easy axis of magnetization on the layering of these CoP multilayers, 14 we can use magnetostriction as an indirect method to determine the critical thickness under which the layers are not well defined, 30 thus, giving crucial information about the interfaces quality. Figure 3 shows that a change in the anisotropy direction has a strong influence in the values of the parameters λHL and λHT . It is important to notice that our experimental set-up only measures changes in the length of the sample along the axis of the cantilever (y-axis in the figure). When considering a film with an out-of-plane easy axis (Figure 3(a)), without applied magnetic field the magnetization is oriented along the perpendicular direction. When applying a magnetic field in the transversal direction (Bx ), there is no component of magnetization along the longitudinal direction. Therefore, no change of length along the longitudinal direction can be measured (λHT = 0). However, when applying a saturating field along the longitudinal direction (By ), magnetization lies along the longitudinal axis and the film is contracted along this direction, measuring a negative value of λHL . The situation is completely different in a film with an in-plane easy axis along the y-direction (Figure 3(b)). Without magnetic field, the magnetization is completely oriented along this direction, the sample is already contracted and there is no change in the longitudinal direction when applying a magnetic field along this direction (λHL = 0). However, when applying a field in the transversal direction (Bx ), magnetization goes out from the longitudinal direction and an elongation is observed, measuring a positive value of λHT . Thus, the behavior of both λHL and λHT gives information about the magnetic anisotropy and, in the case of CoP, this provides an indirect method to extract information about the thickness of the layers forming a multilayer. The experimental evolution of the magnetostriction constant λS , longitudinal 2λHL /3, and



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Figure 3: Schematics of the magnetostrictive behavior of a single layer with out-of-plane anisotropy (a) and a multilayer with in-plane anisotropy (b) when applying a magnetic field in different directions. transverse 2λHT /3 parameters with the thickness of the layers in the multilayers is shown in Figure 4(a). The values are obtained after evaluating the Young modulus of the CoP alloys (155 ± 16 GPa). The first important result to notice is that the magnetostrictive constant, which basically depends on the composition, is approximately the same, λS = −2.0±0.2 ppm, for all measured films. However, λHL and λHT values depend on the layer thickness. In case of Co0.74 P0.26 /Co0.83 P0.17 multilayers, there are two limiting cases in relation with magnetic anisotropy. In the films formed by a single thick Co0.74 P0.26 or Co0.83 P0.17 layer, the easy axis of magnetization lies out of the plane of the film whereas in a multilayered sample with very thin well defined layers, the easy axis of magnetization lies along the plane. This behavior is reflected in Figure 4(a). When the layers are thick (t>500 nm), λHT = 0. When reducing the layer thickness below 500 nm, anisotropy goes from out-of-plane to in-plane longitudinal direction producing a gradual increase of λHT and a gradual decrease of λHL . We have already reported this tendency from 10 to 500 nm. 15 In this paper we explore for the first time the region below 10 nm. 10 ACS Paragon Plus Environment

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From Figure 4(a) it is clear that the tendency in the magnetostrictive constants for samples with layer thicknesses down to 4 nm, is the same as the one previously observed and already reported for samples with layer thicknesses from 500 to 10 nm. This behavior clearly changes below 4 nm and the tendency is reversed. From the previously shown RBS measurements, the interlayer roughness in these CoP multilayers is 3 nm, limiting the possibility of synthesize multilayers with well-defined layers below this value. Therefore, we attribute the behavior observed below 4 nm to the mixing of the layers. The films do not have well defined layers and the magnetic behavior tends to lose the pure in plane magnetic anisotropy arising again the perpendicular anisotropy, which is a fingerprint of a single thick layer. Thus, it is not possible to produce well defined CoP multilayers below 4 nm because the different layers are progressively mixed due to roughness and atom diffusion. The behavior described above is clearly reflected in the magnetic properties of the multilayers. To show the effect, we have plotted in Figure 4(b) the hysteresis loops of selected films. The curves have been measured with a maximum applied magnetic field of 1000 Oe, parallel to the plane of the layers. This field is enough to saturate the samples. Just for clarity, only the central part of the hysteresis loop of the films is shown. The first important thing to be noticed from the magnetic measurements is the already reported behavior in previous works: when the thickness of the layers is large (t=5000 nm), the magnetization processes are mainly due to magnetization rotation which reflects an easy axis perpendicular to the applied magnetic field, i.e. perpendicular to the surface. This easy axis of magnetization moves to the plane when the thickness of the layers decreases (N=500), and the hysteresis loop reflects a magnetization process mainly controlled by domain wall movement. As mentioned before, the behavior below t=4 nm has not been reported. The hysteresis loop corresponding to a sample with t=1 nm has been included in Figure 4(b) to show how the magnetization easy axis moves again out-of-plane for a film whith such a thin layer thickness..



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Conclusions To sum up, in this paper we have shown that RBS is a powerful tool to study the interface quality and layer thickness of amorphous magnetic multilayers with similar composition. In the case of CoP multilayers, we have determined that the different layers are well defined at least for thickness values down to 20 nm. We have measured the magnetrostricion of samples with layers below this thickness, finding a change in the magnetic behavior below 4 nm that we attribute to layer mixing. This value of thickness is similar to the roughness measured by RBS. These measurements provide a lower limit for the control of the magnetic properties of this CoP samples by layering. The results concerning RBS are also interesting because they pave the way to an alternative possibility of studying the interface quality of amorphous multilayers, interfaces that cannot be easily studied by conventional diffraction or electron microscopy techniques.

Acknowledgements Technical support by R. Smith during RBS measurements at CMAM is acknowledged. This work was partially supported by the Ministerio Espa˜ nol de Econom´ıa y Competitividad (MINECO) through the projects MAT2011-28751-C02 and MAT2014-52477-C5-2-P and by the Aragón Regional Government through project E26. S. R-G thanks the MINECO FPI fellowship.

References (1) Butvin, P.; Janosek, M.; Ripka, P.; Butvinová, B.; Svec Sr., P.; Kuzminski, M.; Svec Jr., P.; Janickovic, P.; Vlasak, P. Field Annealed Closed-Path Fluxgate Sensors made of Metallic-Glass Ribbon. Sens. Actuators, A 2012, 184, 72-77.



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(2) Ruhmer, D.; Bogeholz, S.; Ludwig, F.; Schiling, M. Vector Fluxgate Magnetometer for high Operation Temperatures up to 250◦ C. Sens. Actuators, A 2015, 228, 118-124. (3) Karo, H.; Sasada, I. Magnetocardiogram measured by Fundamental Mode Orthogonal Fluxgate Array. J. Appl. Phys. 2015, 117, 17B322. (4) Lei, J.; Wang, T.; Lei, C.; Zhou, Y. Detection of Dynabeds using a MicroElectro-Mechanical System Fluxgate Sensor. Appl. Phys. Lett. 2013, 102, 022413. (5) Sun, X. C.; Yang, Z.; Lei, C.; Guo, L.; Zhou, Y. An Innovative detecting way of Scherichia Coli O157 H:H7 by a Micro-Fluxgate-Based Bio-sensing System. Sens. Actuators, B 2015, 221, 985-992. (6) Pérez, L.; Aroca, C.; Sánchez, P; López, E.; Sánchez, M. C. Planar Fluxgate Sensor with an Electrodeposited Amorphous Core. Sens. Actuators, A 2004, 109(3), 208-211. (7) Kosta, I.; Vallés, E.; Gómez, E.; Sarret, M.; M¨ uller, C. Nanocrystalline CoP Coatings prepared by Different Electrodeposited Techniques. Mater. Lett. 2011, 65(19-20), 2849-2851. (8) da Silva, R. C.; Pasa, A. A.; Mallett, J. J.; Schwarzacher, W. Surface Morphology Evolution during Electrodeposition of Amorphous CoP Films. Surf. Sci. 2005, 576(1-3), 212-216. (9) Sinnecker, J. P.; Knobel, M.; Pirota, K. R. Frequency Dependence of the Magnetoimpedance in Amorphous CoP electrodeposited Layers. J. Appl. Phys 2000, 87, 4825-4827.


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(10) Riveiro. J; Sánchez-Trujillo, M. C.; Magnetic anisotropy of electrodeposited Co-P amorphous allows. IEEE Trans. Magn. 1980, 16, 1426-1428. (11) Rivero, G.; Navarro, I.; Crespo, P.; Pulido, E.; Garcia-Escorial, A.; Hernando, A.; Vazquez, M,: Vallet, M.; Gonzalez-Calbet, J. Magnetic and structural properties of electrodeposited Co1−x Px amorphous ribbons. J. Appl. Phys 1991, 69, 5454-5456. (12) Riveiro. J; Rivero, G. Multilayeres magnetic amorphous Co-P films. IEEE Trans. Magn. 1981, 17, 3082-3084. (13) Favieres, C; Aroca, C; Sánchez, M. C.; Madurga, V. Continuous change of surface magnetization direction from perpendicular to planar in soft magnetic CoP multilayers. J. Appl. Phys 2002, 91, 9995-10002. (14) Pérez, L.; de Abril, O.; Sánchez, M. C.; Aroca, C.; López, E.; Sánchez, P. Electrodeposited Amorphous CoP Multilayers with high Permeability. J. Magn. Magn. Mater. 2000, 215-216, 337-339. (15) Ciudad, D.;Prieto, J. L.; Lucas, I.; Aroca, C.; Sánchez, P. Optimization of Magnetic Properties of Electrodeposited CoP Multilayers for Sensor Applications. J. Appl. Phys. 2007, 101, 043907. (16) Lucas, I.; Pérez, L.; Plaza, M.; de Abril, O.; Sánchez, M. C. Pinning Field and Coercivity in CoP Alloys. J. Magn. Magn. Mater. 2007, 316(2), 462464. (17) Cziráki, A.; Pierron-Bohnes, V.; Ulhaq-Bouillet, C.; Tóth-Kádár. E.; Bakonyi, I. Kinetic versus Thermodynamic Control over Growth Process of Electrodeposited Bi/BiSb Superlattice Nanowires. Nano Lett. 2008, 8(5), 1286-1290.



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(18) Reyes, D.; Biziere, N.; Warot-Fonrose, B:; Wade, T.; Gatel, C. Magnetic Configurations in Co/Cu Multilayered Nanowires: Evidence of Structural and Magnetic Interplay. Nano Lett. 2016, 16(2), 1230-1236. (19) Escobar Galindo, R.; Gago, R.; Duday, D.; Palacio, C. Towards nanometric resolution in multilayer depth profiling: a comparative study of RBS, SIMS, XPS and GDOES. Anal Bioanal Chem 2010, 396, 2725-2740. (20) Prieto, P.; Marco, J .F.; Sanz, J. M. Synthesis and characterization of iron nitrides. An XRD, Mossbauer, RBS and XPS characterization. Surf. Interf. Anal. 2008, 40, 781-785. (21) Mayer. M. SIMNRA user’s guide. Tech. Rep. IPP 9/113, Max-PlanckInstitut fur Plasmaphysik, Garching, 1997. (22) Ziegler, J. F.; Biersack, J. P. ; Littmark, U. SRIM - The Stopping and Range of Ions in Matter. Pergamon Press, New York 1985. (23) Parkes. D. E.; Shelford, L. R.; Wadley, P.; Holy, V.; Wang, M.; Hindmarch. A. T.; van der Laan, G.; Campion, R. P.; Edmonds, . W.; Cavill. S. A.; Rushforth, A. W.; Magnetostrictive thin films for microwave spintronics Sci. Rep. 2015, 5, 13621. (24) Jammalamadaka, S. N.; Kuntz, S.; Berg, O.; Kittler, W.; Kannan, U. M.; Chelvane, J. A.; Surgers, C. Remote control of magnetostriction-based nanocontacts at room temperature. Sci. Rep. 2013, 3, 2220. (25) Gibbs, M. R. J.; Hill, E. W.; Wright, P. J. Magnetic materials for MEMS applications. J. Phys. D: Appl. Phys. 2004, 37, R237-R244. (26) Tam, A. C.; Schoeder, H. Precise Measurements of a Magnetostriction


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Coefficient of a Thin Soft-Magnetic Film deposited on a Substrate. J. Appl. Phys. 1988, 64, 5422-5424. (27) Tam, A. C.; Schoeder, H. A New High-Precision Optical Technique to measure Magnetostriction of a Thin Magnetic Film deposited on a Substrate. IEEE Trans. Magn. 1989, 25(3), 2629-2638. (28) González-Guerrero, M.; Prieto, J. L.; Ciudad, D.; Sánchez, P.; Aroca, C. Engineering the Magnetic Properties of Amorphous (Fe

80 Co20 )80 B20

with

Multilayers of Variable Anisotropy Direction. Appl. Phys. Lett. 2007, 90, 162501. (29) Ranchal, R.; Gutiérrez-D´ıez, V.; González-Mart´ın, V. Influence of the TbFe2 Crystallization on the Magnetic and Magnetostrictive Properties of (Fe3 Ga/TbFe2 )n Heterostructures. Acta Mater. 2012, 60(4), 1840-1845. (30) Lanotte, L.; Iannotti, V. Magnetoelastic Effects at the Interface of CoP Nanostructured Multilayers. Il Nuovo Cimento D 1995, 17(3), 279-288.



Co0.74P0.26/Co0.83P0.17 Multilayers

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Energy (KeV) 200 400 600 800 1000 1200 1400 Co+P+O

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Assessment of Layer Thickness and Interface Quality in CoP

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