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Structure, Microstructure, and Magnetism of Electrodeposited Fe70Pd30 Nanowires Veronika Haehnel,†,‡ Christine Mickel,† Sebastian Fa¨hler,† Ludwig Schultz,†,‡ and Heike Schlo¨rb*,† IFW Dresden, P. O. Box 270116, 01171 Dresden, Germany, and Faculty of Mechanical Engineering, TU Dresden, 01062 Dresden, Germany ReceiVed: August 16, 2010; ReVised Manuscript ReceiVed: October 6, 2010
Fe-Pd nanowires for MSM applications are obtained by electrodeposition from a stable complexed Fe3+/ Pd2+ electrolyte. By application of an alternating potential mode, a composition close to the intended Fe70Pd30 alloy can be achieved. In particular, the second pulse step potential E2 is identified to be the key parameter for continuous, defect-free nanowires. The adjustment of E2 to more positive values avoids the formation of Pd-rich segments as well as the blocking of pores by hydrogen bubbles. Detailed TEM and structural investigations reveal a bcc Fe-Pd structure and nanocrystalline deposits with grain sizes in the 5 nm range. The observed structural features are attributed to the electrochemical processes within the constraint geometry of the nanoporous template. The magnetic properties of these nanowires are controlled by shape anisotropy as well as magnetostatic interactions. Introduction Martensitic transforming Fe-Pd alloys centering around the composition Fe70Pd301 are of increasing scientific and technological interest as they show the thermal2 as well as the magnetic shape memory (MSM) effect.3 Both effects result in strains up to several percent, which makes this material system of particular interest for micro- and nanoactuators, as well as sensors. While the high application potential motivated intense research on thin films,4-6 the benefits of nanowires are obvious: For the thermal shape memory effect nanowires are expected to reach a high maximum actuation frequency that is attributed to fast cooling due to their high surface to volume fraction. When using the magnetic shape memory effect, the lower eddy current losses at a reduced size are also expected to be beneficial for an increased frequency.7 For the novel SFIM actuation mode (“stray-field induced microstructure8”), the maximum strain is expected to double in nanowires, as shape anisotropy favors only a single wire axis compared to thin films where both inplane directions are equally favored. Fe-Pd films are commonly grown by physical deposition methods6,9,10and can be lifted off using sacrificial layer technology.4 Lithographic methods might then be used to produce nanowires. A much more efficient way to prepare nanowires is to use electrodeposition within nanoporous templates, which produces on the order of 109 nanowires in a single run.11-13 Single element nanowires of Fe and Pd can be routinely achieved from single ion electrolytes such as FeSO4 solutions14,15 and PdCl2 solutions,16,17 respectively. The electrochemical codeposition of Fe and Pd is challenging due to the large difference in nobility, and therefore the standard potentials of Pd (Pd2+/Pd: E0 ) 0.95 V18) and Fe (Fe2+/Fe: E0 ) -0.447 V18). The standard potential of Pd2+ is moved to more negative values ([Pd(NH3)4]2+/Pd: E0 ) 0.00 V)19 by complexing, easing the codeposition of both ions.20 Nevertheless, the electroless reaction 2Fe2+ + Pd2+ f 2Fe3+ + Pd produces Pd nuclei that * To whom correspondence should be addressed. Phone: +49 351 4659 230. Fax: +49 351 4659 9 230. E-mail:
[email protected]. † IFW Dresden. ‡ TU Dresden.
are easily deposited at any suitable nucleation sites within the electrolyte container. It has been shown that exchanging Fe2+ by Fe3+ can completely avoid this reaction and therefore significantly stabilize the electrolyte.21 Also, hydrogen evolution as a side reaction has to be avoided, since gas bubbles within the pores might block the pores and therefore interrupt the metal deposition. By applying pulse plating techniques13 it has been shown that pore blocking can be reduced. Additionally, the hydrogen evolution results in the formation of a high number of OH- ions within the pores leading to facile precipitation of hydroxides, in particular Fe(OH)3. By adding 5-sulfosalicylic acid,22-25 a stable Fe3+ complex26 is formed that prevents hydroxide formation. Based on these considerations, it has recently been shown that continuous long nanowires close to the desired composition Fe70Pd30 can be obtained within nanoporous alumina templates.21 Nonetheless, a certain number of defects and composition variations were still observed. The objective of this study is to identify the origin of these defects and to correlate compositional and structural features of Fe-Pd nanowires with the applied deposition potentials. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and high-resolution electron microscopy investigations are combined and evaluated in order to identify the relevant electrochemical processes within the constrained geometry of the nanoporous template. As a key step toward MSM nanoactuators, a route for defect-free nanowires with homogeneous composition has been developed by adjusting the deposition potentials in the alternating potential mode. Experimental Section The preparation of anodic alumina arrays is carried out by the well-known two-step anodization process which creates hexagonally ordered nanopores,27 a detailed description of which can be found elsewhere.28 To obtain free-standing membranes, remaining aluminum and the barrier layer were removed by chemical etching using CuCl2 and H3PO4. The typical pore diameter DP is roughly 70 nm, and the pore length is between 20 and 25 µm. Next, a 200 nm thick Au layer was sputterdeposited onto the backside of the alumina membrane to provide
10.1021/jp1077455 2010 American Chemical Society Published on Web 10/22/2010
Electrodeposited Fe70Pd30 Nanowires
J. Phys. Chem. C, Vol. 114, No. 45, 2010 19279 using a FEI Tecnai T20 transmission electron microscope operating at 200 kV. This was combined with EDX spectroscopy to determine the chemical composition with high spatial resolution. Using a vibration sample magnetometer (VSM insert for Quantum Design PPMS), magnetization curves in fields up to 3 T parallel and perpendicular to the wire axis were measured. Results
Figure 1. XRD diagrams (Co KR radiation) of electrodeposited Fe-Pd nanowires deposited at different off-potentials E2. The lines mark the reflection positions calculated from literature values: Fe-Pdfcc and Fe-Pdfct (Fe71.5Pd29.5).10,29
electrical contact and serve as a working electrode for electrodeposition. An aqueous electrolyte containing 0.02 M Pd(NH3)4Cl2, 0.1 M Fe2(SO4)3*9H2O, 0.25 M C7H6O6S*2H2O, and 0.3 M (NH4)2SO4 was used for the nanowire deposition,21 where the pH was adjusted to 5 for all experiments. The electrodeposition experiments were exclusively performed at room temperature using a typical three electrode arrangement, where a Pt foil was used as counter electrode and the reference electrode was a saturated calomel electrode (SCE, 241 mVSHE), noting that all electrode potentials are in reference to the potential of the SCE. Electrodeposition was carried out in pulsed potential mode using an EG&G Potentiostat/Galvanostat model 263A in which two alternating potential steps E1 and E2 were applied for t1 ) 60 s and t2 ) 180 s and repeated 30 times. Here, E1 was kept constant at -1.1 V, whereas E2 was varied between -0.5 and -0.1 V. The crystalline structure was investigated by X-ray diffraction (Phillips X’pert PW 3400, Co KR radiation) in a Bragg-Brentano geometry on the backside of the membrane after removing the Au layer. The nanowire morphology and integral composition were examined at cross-sectional membrane areas by highresolution scanning electron microscopy combined with energy dispersive X-ray spectroscopy (HR-SEM Leo 1530 Gemini/ Zeiss with EDX X-Flash detector, Esprit, Bruker system). For transmission electron microscopy, the samples were mechanically polished with a modified tripod to a thickness of approximately 10 µm and subsequently thinned by Ar ion milling at small angles and low energy using a Leica RES101 system. The investigation of the nanowires was accomplished
Fe-Pd nanowires were electrodeposited in the pulsed potential mode with various off-potentials E2. The X-ray diffraction patterns used to determine their crystal structure are presented in Figure 1. The observed XRD reflection at around 2θ ) 50.8° is close to the theoretical position of the (110) bcc reflection of Fe75Pd25 at 2θ ) 50.57°. The absence of other bcc reflections reveals a preferred (110) orientation along the wire axis. No indication for a fct martensitic phase is found. The low intensity may be attributed to a fine grain size approaching nanocrystalline size, whereas the peak broadening possibly to internal stresses and/or chemical heterogeneities. Though these integral measurements yield similar crystal structure independent of the applied off-potential and no signature of impurity phases is observed, we find that the morphology on a local scale differs significantly. Our cross-sectional HR-SEM micrographs in Figure 2 display differences in morphology and microstructure that are expected to strongly influence the properties of the wires. Samples prepared at E2 ) -0.5 V (Figure 2a) and -0.3 V (Figure 2b), respectively, still indicate some contrast within the wires which presumably originates from a difference in composition (marked by arrows in Figure 2) as well as a decreasing number of discontinuities and short wire fragments of only 90-180 nm length within otherwise empty pores. All these features are absent in the sample prepared at E2 ) -0.1 V. Here an increased filling factor and a lack of defects are detected by scanning electron microscopy. The nanowire arrays composition as determined by the EDX system within the SEM is close to the intended composition Fe70Pd30 (Figure 3), where a slight increase in Fe-content for more positive potentials is observed. These composition values only represent an integral value, because the penetration depth is in the range of micrometers and by far exceeds the dimension of a single nanowire. Therefore, narrow changes in composition, as expected for the marked contrasts in Figure 2, are not accessible by this method. The oxygen content is not determinable in this way as the aluminum oxide acting as a matrix for the nanowires is contributing in these integral measurements. As nanoactuator applications require reproducible defect-free nanowires with homogeneous composition, a detailed correlation of the local composition, structure, and microstructure with deposition parameters is essential. This is done by means of
Figure 2. Cross-sectional HR-SEM micrographs of an alumina template filled with Fe-Pd nanowires, deposited using (a) E2 ) -0.5 V, (b) E2 ) -0.3 V, and (c) E2 ) -0.1 V. Each left image shows the continuity and length of the nanowires, each right image the more detailed microstructure. The arrows mark the observed material contrast.
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Figure 3. Integral composition of Fe-Pd nanowire arrays obtained by EDX as a function of off-potential E2. The horizontal lines mark the intended composition Fe70Pd30.
Figure 4. Microstructure of Fe-Pd nanowires deposited using E2 ) -0.3 V. (a) Bright-field TEM micrograph. A marks an intersection within a nanowire; B is a partially empty pore. (b) SAD pattern indexed with a bcc structure.
TEM investigations (Figure 4) and discussed with respect to electrochemical processes within the constraining geometry of a nanoporous template. Figure 4a presents a TEM overview of a sample deposited at E2 ) -0.3 V. The average nanowire composition was found to be Fe71Pd29 ((4 atom %). The pore walls consisting of alumina and the Fe-Pd filled pores are marked by arrows. Whereas the overall nanowire morphology is predominantly continuous, TEM confirms the appearance of discontinuities (marked as A in Figure 4a) or partially empty pores (marked as B in Figure 4a). Different contrasts within the nanowires, e.g., black spots, are due to different grain orientations. The typical crystallite sizes are around 5 nm diameter, while sometimes clusters of 15-20 nm in size can be observed. This nanocrystallinity is also observed using selected-area diffraction (SAD, Figure 4b). The continuous ring pattern in the diffraction image again implies nanocrystalline grain sizes, where discrete spots along the (110) ring prove the existence of larger grains. Further detailed analysis using STEM-EDX and nanodiffraction of a conveniently situated crystal (indicated with the arrow in Figure 5a) revealed a local composition of Fe67Pd33 and bcc Fe75Pd25 (110) reflections with a [111] zone axis (Figure 5b). The above-mentioned defects have also been investigated in detail. Particularly in small areas above the constrictions (marked as A in Figure 4a) an increased Pd content up to about 84 atom % was observed. Even higher Pd contents of more than 98 atom % and almost no Fe were observed in the short wire segments (see Figure 5c). Nanodiffraction of these areas reveals a crystal structure corresponding to fcc Pd with [121] zone axis (Figure 5d). In contrast, no defects at all are obtained in the TEM investigations of Fe-Pd nanowires deposited at E2 ) -0.1 V (Figure 6a). EDX-TEM measurements yield an average
Figure 5. Local microstructure and structure of Fe-Pd nanowires obtained at E2 ) -0.3 V: (a) bright-field TEM micrograph of long and continuous Fe67Pd33 nanowires; (b) nanodiffraction pattern of one crystal of bcc structure with [111] zone axis; (c) bright-field TEM micrograph of a short nanowire segment; (d) nanodiffraction pattern of one crystal of fcc Pd with [121] zone axis.
composition of Fe71Pd29 ((4 atom %). As in the other sample, SAD exhibits a continuous ring pattern of bcc crystal structure similar to Fe75Pd25. Some points with higher intensity are found on the (110) ring reflecting the presence of some larger crystals. Nanodiffraction again shows the reflection pattern of a bcc Fe75Pd25 crystal with [111] zone axis. Fine grain sizes around 7 nm (between 3 and 12 nm, see Figure 6b) have been measured. As an additional feature, fine strained crystals become visible by high-resolution TEM (Figure 6b) that might serve as a possible reason for the peak broadening observed by X-ray diffraction. The magnetic behavior of the nanowire arrays obtained from VSM measurements is depicted in Figure 7. In general, all samples show a similar behavior. When applying the field parallel to the wire axis, saturation polarization is achieved in low fields. In contrast to this, a high field is required to saturate magnetization perpendicular to the wire axis. This observation reflects shape anisotropy, which favors alignment of magnetization along the wire axis. The anisotropy field evaluated from the field required to saturate the sample magnetization in the hard axis loop is µ0HA ≈ 0.72...0.62 T for the respective samples with increasing E2. For high aspect ratio nanowires (the present aspect ratio is roughly 150), this is a good measure of spontaneous polarization.15 When using the spontaneous polarization JS ) 1.66 T of bulk Fe70Pd30,30 one expects µ0HA ) Js/2 ) 0.83 T. The observed agreement of measured and calculated HA indicates that only a small fraction of (nonmagnetic) impurities is present within the nanowires. Before analyzing the magnetization curves along the wire axis, it is worthwhile to compare this field with the other anisotropies involved. Magnetocrystalline aniosotropy field is negligible, even if some tetragonally distorted bcc phase would be present (µ0Hmagnetocrystalline < 50 mT35). Due to the observed grain size of
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Figure 6. (a) Bright-field TEM micrograph of Fe-Pd nanowires deposited using E2 ) -0.1 V. (b) High-resolution TEM micrograph of a Fe-Pd nanowire revealing fine crystallites between 3 and 12 nm and fine tensed grains (stripe pattern, indicated with arrows).
Figure 7. Magnetization curves of Fe-Pd nanowire arrays in alumina template deposited at various off-time potentials E2. Measurements are shown for both field directions, along and perpendicular to the wire axis.
Figure 8. Freestanding Fe-Pd nanowires (E2 ) -0.5 V) as obtained after dissolving the alumina matrix.
7 nm, exchange coupling is expected to average out most of this magnetocrystalline anisotropy (for a detailed discussion of the random anisotropy model for Fe-Pd, see ref 10). Magnetostatic interactions between neighboring nanowires, however, are important. They favor an antiferromagnetic alignment of neighboring nanowires, since this would allow an easy flux closure. Recently, a simple model had been suggested, which
uses the template geometry in order to estimate the field acting on neighboring nanowires.31 For the present geometry this gives -0.46 T (using JS ) 1.66 T of bulk Fe70Pd3030). This is about half the shape anisotropy, which strongly influences the magnetization curves perpendicular to the wire axis. In particular for the wires deposited at E2 ) -0.1 V, exhibiting the most ideal morphology, no rectangular loop expected for a ferromagnet along its easy axis is observed along the wire axis, but magnetization decreases already in positive fields. To understand the role of magnetostatic interactions, one may consider the sample consisting of antiferromagnetically coupled macrospins having a huge uniaxial anisotropy ()shape anisotropy of each ferromagnetic nanowire). The presence of two relevant length scales (ferromagnetic order within each wire and antiferromagnetic coupling between the wires) results in an integral magnetization curve which is closer to an antiferromagnet than a ferromagnet. Indeed coercivity is as low as 42 mT. These concepts also allow an explanation of the different magnetization curves observed for wires deposited at -0.5 or -0.3 V. Here, nanowires are interrupted by short, nonmagnetic Pd-rich sections. This facilitates the formation of magnetic domains within one nanowire and allows magnetostatic interactions between these segments. Compared to the homogeneous nanowires obtained at -0.1 V, a partial flux closure within each wire is possible, reducing the stray field between neighboring wires. The reduced influence of magnetostatic interactions between the wires results in a more rectangular hysteresis curve along the wire axis but does not alter the magnetization curve along the hard axis. Since the aim of the present paper is to approach an ideal nanowire geometry, a more detailed study, which can, e.g., be performed by angular dependent measurements,32 is beyond the scope of the present paper. Finally, it has been successfully demonstrated that highly stable freestanding nanowires as required for nanoactuators can be obtained after dissolving the alumina template in 1 M NaOH (Figure 8). The nanowires are stable and can be easily handled with microtweezers. Discussion It has been previously shown that both pure Fe15 as well as Fe-Pd alloy nanowires near the intended composition Fe70Pd3021 can be electrochemically prepared at a deposition potential of E ) -1.1 VSCE. While it is generally accepted that pulse plating can improve nanowire morphology due to an enhanced diffusion
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within the template,13 the following analysis will show that for noble metals like Pd their catalytic activity must be considered as well. A significant disadvantage of applying such a negative deposition potential is hydrogen evolution due to H3O+ reduction and water decomposition. To avoid accumulation of large gas bubbles that may block the pores and disrupt the nanowire growth, the deposition is suspended by introducing a second, more positive potential step. This off-potential step E2 is intended to remove undesired gas bubbles, while neither Fe nor Pd should be deposited during this off-time.21 Significant redissolution of previously deposited metal should also be avoided, as this may cause irregular wire morphologies, e.g., holes, pits, or fissured endings. Electrochemical experiments (that are beyond the scope of this study and will be published elsewhere) suggested that a suitable off-potential should be in the range -0.5 V e E2 e -0.1 V. When using common integral methods like XRD and SEM-EDX, almost no impact of E2 on the nanowire quality can be found. At higher resolutions key differences in nanowire morphology are observed, which are expected to have an impact on future application as MSM nanoactuators. These differences are clearly correlated with the off-potential E2 and will be discussed in the following in terms of possible electrochemical processes. The overall number of irregularities decreases with increasing E2, and almost no defects or inhomogeneities are found at E2 ) -0.1 V. This goes along with the measured current during the off-time step that is slightly cathodic for -0.5 V21 and -0.3 V and almost zero at -0.1 V. Hence, the observed short Pdrich sections whose number along the complete nanowire is identical to the number of applied pulses must be generated during the off-time step, where no Fe deposition can occur. The most probable mechanism for the deposition of Pd at these potentials is the reduction of the few remaining uncomplexed Pd2+ ions still present in the electrolyte. Further possibities might be an underpotential deposition of [Pd(NH3)4]2+ ions, the facilitated reduction of intermediate state Pd2+ complexes, or the formation of hardly soluble Pd(NH3)2Cl2.33 The length of these areas is marginal, however, compared to the continuous wire length because of the low growth rate for Pd deposition at low concentrations and low overpotentials. The small number and size of the Pd segments and resulting low intensity can explain why no Pd reflections are visible in the XRD measurements. The observed constrictions and partially empty pores can be a direct consequence of the described Pd deposition. First, the catalytic effect of freshly deposited Pd is expected to enhance hydrogen evolution. This can result in a complete blocking of pores, in particular above Pd-rich areas as shown in Figure 4a, marked with B, and Figure 5c. Second, hydrogen bubbles that are evolved during the deposition step E1 are expected to disappear from the pores during the subsequent off-time step E2. The described deposition of Pd during E2 may hinder the complete removal of these hydrogen bubbles. This may explain the small constrictions below Pd-rich areas as marked with A in Figure 4a. At E2 ) -0.1 V, neither Pd-rich areas nor defects are observed, indicating that this potential is suitable to avoid the undesired Pd deposition completely. So far no indication of a martensitic phase or a magnetic shape memory effect had been observed. Furthermore, the observed bcc phase is not expected for a composition above 30 atom % Pd. We attribute this to the nonequilibrium deposition conditions which result in grain sizes below 10 nm. As analyzed
Haehnel et al. by Waitz et al.,34 a martensitic transformation can be suppressed at grain sizes below roughly 60 nm. Annealing Fe-Pd at temperatures above 900 °C can result in a significantly increased grain size.35 Once the grain sizes reach or exceed the wire diameter, one expects less constraints from neighboring grains. This should allow both a martensitic transformation as well as the magnetic shape memory effect. For Ni-Mn-Ga microfibers, for example, this allowed the obtaining of about 1% strain by an external magnetic field.36 Conclusion The suitability of pulsed electrodeposition in alumina templates to obtain long and continuous nanowires close to the intended Fe70Pd30 composition is demonstrated. As a stable electrolyte, a sulfosalicylic-ammonia-complexed solution containing Fe3+ and Pd2+ was used. The obtained nanowires reveal a body-centered cubic structure with grain sizes in the 5 nm range. Composition discontinuities such as Pd-rich areas and short segments are attributed to undesirable reduction reactions during the second potential step E2 in the pulse deposition mode. After adjusting the off-potential E2 to more positive values and, therefore, avoiding these reactions, stable defect-free nanowires with homogeneous composition have been obtained. Magnetism of these nanowires is controlled by shape anisotropy as well as magnetostatic interactions between neighboring nanowires. These results are very promising as a starting point for future research toward MSM nanoactuators. Acknowledgment. We thank S. Neitsch for alumina template preparation and G. Scheider for TEM sample preparation. The Deutsche Forschungsgemeinschaft (DFG) is acknowledged for financial support (SPP 1165, SCHL 589/2). References and Notes (1) Hultgren, R.; Zapffe, C. A. Nature 1938, 142, 395. (2) Sohmura, T.; Oshima, R.; Fujita, F. E. Scr. Metall. 1980, 14 (8), 855. (3) James, R. D.; Wuttig, M. Philos. Mag. A 1998, 77 (5), 1273. (4) Bechthold, C.; Buschbeck, J.; Lotnyk, A.; Erkartal, B.; Hamann, S.; Zamponi, L. S. C.; Ludwig, A.; Kienle, L.; Fa¨hler, S.; Quandt, E. AdV. Mater. 2010, 22, 4629. (5) Kakeshita, T.; Fukuda, T. Mater. Sci. Forum 2002, 394-395, 531. (6) Inoue, S.; Inoue, K.; Koterazawa, K.; Mizuuchi, K. Mater. Sci. Eng. 2003, A339, 29. (7) O’Handley, R. C. Modern Magnetic Materials: Principles and Application; John Wiley & Sons: New York, 2000. (8) Thomas, M.; Heczko, O.; Buschbeck, J.; Lai, Y. W.; McCord, J.; Kaufmann, S.; Schultz, L.; Fa¨hler, S. AdV. Mater. 2009, 21 (36), 3708. (9) Vokoun, D.; Hu, C. T. Scr. Mater. 2002, 47 (7), 453. (10) Buschbeck, J.; Lindemann, I.; Schultz, L.; Fa¨hler, S. Phys. ReV. B: Condens. Matter Mater. Phys. 2007, 76 (20), 205421. (11) AlMawlawi, D.; Coombs, N.; Moskovits, M. J. Appl. Phys. 1991, 70 (8), 4421. (12) Zeng, H.; Zheng, M.; Skomski, R.; Sellmyer, D. J.; Liu, Y.; Menon, L.; Bandyopadhyay, S. J. Appl. Phys. 2000, 87 (9), 4718. (13) Nielsch, K.; Mu¨ller, F.; Li, A. P.; Go¨sele, U. AdV. Mater. 2000, 12 (8), 582. (14) Sellmyer, D. J.; Zheng, M.; Skomski, R. J Phys.: Condens. Matter 2001, 13, R443. (15) Haehnel, V.; Fa¨hler, S.; Schaaf, P.; Miglierini, M.; Mickel, C.; Schultz, L.; Schlo¨rb, H. Acta Mater. 2010, 58 (7), 2330. (16) Kim, K. T.; Cho, S. M. Mater. Lett. 2006, 60, 352. (17) Wang, H.; Xu, C.; Cheng, F.; Jiang, S. Electrochem. Commun. 2007, 9, 1212. (18) Schlesinger, M.; Paunovic, M. Modern Electroplating; John Wiley & Sons: New York, 2000. (19) Baumga¨rtner, M. E.; Gabe, D. R. Trans. IMF 2000, 78 (2), 79. (20) Landolt, D. Surf. Finish. 2001, 88 (9), 70 Plat. (21) Haehnel, V.; Fa¨hler, S.; Schultz, L.; Schlo¨rb, H. Electrochem. Commun. 2010, 12, 1116. (22) Juzikis, P.; Kittel, M.; Raub, C. Plat. Surf. Finish. 1994, 81 (8), 59.
Electrodeposited Fe70Pd30 Nanowires (23) Bryden, K. J.; Ying, J. Y. Nanostruct. Mater. 1997, 9 (1-8), 485. (24) Fei, X.; Tang, S.; Wang, R.; Su, H.; Du, Y. Solid State Commun. 2007, 141 (1), 25. (25) Takata, F. M.; Pattanaik, G.; Soffa, W. A.; Sumodjo, P. T.; Zangari, G. Electrochem. Commun. 2008, 10 (4), 568. (26) Banks, C. V.; Patterson, J. H. J. Am. Chem. Soc. 1951, 73, 3062. (27) Li, A. P.; Mu¨ller, F.; Birner, A.; Nielsch, K.; Go¨sele, U. J. Appl. Phys. 1998, 84 (11), 6023. (28) Kumar, A.; Fa¨hler, S.; Schlo¨rb, H.; Leistner, K.; Schultz, L. Phys. ReV. B 2006, 73 (6), 064421. (29) Cui, J.; Shield, T.; James, R. Acta Mater. 2004, 52, 35. (30) Kussmann, A.; Jessen, K. J. Phys. Soc. Jpn. 1962, 17, 136.
J. Phys. Chem. C, Vol. 114, No. 45, 2010 19283 (31) Schlo¨rb, H.; Haehnel, V.; Khatri, M. S.; Srivastav, A.; Kumar, A.; Schultz, L.; Fa¨hler, S. Phys. Status Solidi B 2010, 247 (10), 2364. (32) Han, G. C.; Zong, B. Y.; Luo, P.; Wu, Y. H. J. Appl. Phys. 2003, 93, 9202. (33) Hedrich, H. D.; Raub, C. J. Surf. Technol. 1979, 8, 347. (34) Waitz, T.; Kazykhanov, V.; Karnthaler, H. P. Acta Mater. 2004, 52 (1), 137. (35) Buschbeck, J.; Hamann, S.; Ludwig, A.; Holzapfel, B.; Schultz, L.; Fa¨hler, S. J. Appl. Phys. 2010, 107, 113919. (36) Scheerbaum, N.; Heczko, O.; Liu, J.; Hinz, D.; Schultz, L.; Gutfleisch, O. New J. Phys. 2008, 10, 073002.
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