The electrodeposition of NiFe nanowires-with the length ∼3.0 μm and diameter 200 nm-using the porous anodized aluminum oxide (AAO) templates on the sputtered Au-back electrode (300 nm) using sulfate/chloride electrolyte solution and potential pulsed deposition. The electrode area of Au-AAO template, determined by the reversible one-electron transfer oxidation of K 4 Fe(CN) 6 , used as a probe in CV, was found to be ∼2.4 times larger than Au-thin film electrode. The anomalous codeposition phenomenon known as a ,,volcano" type curve-with a maximum in Fe-content in NiFe as a function of the applied potential-was observed in the literature. The observed results were explained through the limited mass transport of Fe +2 ions after the peak. This explanation is partially correct, but not complete. The electrodeposition of NiFe nanowire in this work resulted in a similar "volcano" type curve. The alternative explanation of anomalous codeposition-through the surface concentration of H + dependent adsorption/desorption of FeOH + and NiOH + electroactive species-was proposed. The electrodeposition of NiFe nanowire arrays using a designed pulse potential method produced fcc NiFe nanowires with 5-55% Fe with controlled composition, length, and uniformity.The distinct decrease of parallel coercivity of NiFe nanowire arrays having the same length was observed with increase of Fe-content in NiFe, which also correlates with the increase of their magnetic saturation. 12 The studies on magnetic properties of NiFe nanowire arrays were intensified during last 15 years. [13][14][15][16][17][18][19][20] The electrodeposition of NiFe alloys exhibits a phenomenon known as an anomalous codeposition, which is characterized by the anomaly that less noble metal, i.e. Fe, deposits preferentially. 21 The extent of anomalous codeposition can be evaluated by the "selectivity ratio" (SR), which is defined as an atomic ratio of Fe/Ni in the deposit to the molar ratio of Fe +2 /Ni +2 in the electrolyte. 22 The SR is dependent on solution condition (pH, presence of organic additives, concentration of electrolytes, temperature, etc), method of electrodeposition (constant current density, controlled potential, pulsed current or potential), and the thickness of deposit. The value of SR ranges from 1.0 (for non-anomalous codeposition) to 15 (for anomalous codeposition). The variation of composition of NiFe films affects the following properties of deposit: (i) stress, 23 (ii) magnetostriction, 24 (iii) crystal structure, 25 and (iv) grain size. 26 Thereby, the resulting changes profoundly influence the magnetic behavior of electrodeposited NiFe alloys, which was demonstrated recently. 27The present work describes the method of electrodeposition of NiFe nanowires into anodized aluminum oxide (AAO) templates with the controlled elemental composition using designed potential pulse electrodeposition. We report here a new explanation for the observed anomalous codeposition of NiFe in nanowires, through the surface concentration of H + dependent adsorption/...

Among all transition metals magnetic alloys, Co 35 Fe 65 possesses the highest saturation magnetization B S = 2.45 T at room temperature given by the so-called "Slater-Pauling limit". For controlled electrodeposition of Co 35 Fe 65 nanowire arrays the following parameters were found to be optimal: electrolyte solution with 1-2 mM malonic acid (MA), ionic ratio Fe +2 /Co +2 = 2.0, growth rate, and pulsed potential deposition with time-on (2.5 s) at the potential of −1.15 V/SCE and time-off (1.0 s) at −0.70 V/SCE. These arrays were deposited inside anodic aluminum oxide (AAO) templates that contained columnar nanopores with diameters either 35 or 200 nm. Cyclic voltammetry was used in solution with and without MA and reaction mechanism was proposed to explain the critical role of MA in electrodeposition of CoFe alloys. In addition to uniform deposition of stechiometric Co 35 Fe 65 alloys, a selectivity ratio, (SR) ∼1.0, were achieved, which means that the atomic ratio of Fe/Co in the nanowire matched the molar ratio of Fe +2 /Co +2 in the electrolyte. The magnetic behavior of the subsequent 2.45 T Co 35 Fe 65 nanowire arrays showed that the shape and magnetostatic anisotropies dominated the effective anisotropy, and the impact of magnetocrystalline and magnetelastic anisotropies field was very small. 1 The highest saturation magnetization of all transition-metal (TM) alloys at room temperature shows Co 36 Fe 65 alloy with respective saturation magnetization of B s = 2.45 T, which is commonly referred to us as the "Slater-Pauling limit".2 Thin films of these alloys, obtained either by electrochemical deposition (ED) or called sputter deposition, are currently used in high areal recording density (HRD) heads including longitudinal (LMR), perpendicular (PMR), and heat assisted (HAMR) magnetic recording. In fact, about 15 years ago Seagate Technologies was first in the recording head industry to introduce 2.4 T CoFe as the longitudinal writer pole material-which was fabricated by electrodeposition. 3 The advantages of electrochemical vs. sputtering deposition include reduced process content, reduced variance and reduced cost. Importantly, controlled electrodeposition is possible even into high aspect ratio of templates including anodized aluminum oxide-AAO, diblock copolymers-DBC, carbonate membranes, and porous silicone. Porous AAO templates are particularly attractive since the pore diameters can be 10-300 nm with pore densities in the range of 10 9 to 10 11 cm −2 . 4 Ferromagnetic nanowire arrays have been used as a miniaturized devices in electronics and optics. 5 In addition, such nanowires have a promising biomagnetic applications like biosensing, cell separation, MRI contrast agents and magnetic hyperthermia. [6][7][8][9][10] Most biomagnetic studies have been limited to nanometer iron-oxide based nanoparticles for MRI imaging and magnetic hyperthermia.6 However, the low saturation magnetization of the bulk iron-oxides (e.g. B s ∼0.5 T for Fe 2 O 3 11 ) prevents them from becoming highly efficient in hypertherm...

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Fe79.7−xNb0.3CrxB20 (x = 11.5–13.5 at. %) submicron powders with glassy structure and sizes between a few tens of nm and 1 μm have been prepared by high-energy ball milling from glassy melt-spun ribbons (MSRs) precursors. The glassy structure existing in the MSRs, and consisting of Fe-Cr clusters embedded within the (Fe,Nb)3B residual amorphous matrix, is preserved by milling the annealed MSRs in oleic acid and n-heptane. The glassy structure of the submicron powders confers the specific magnetic properties and allows tuning the Curie temperatures in the range of 15–50 °C. The precipitation of α-Fe in excess shifts the Curie temperature to 780 °C. The use of surfactants (oleic acid or heptane) avoids partially the agglomeration of powders, and their individual size goes down to 25–40 nm. The heating efficiency of the submicron powders in a.c. fields (H = 350 mT and f = 153 kHz) evidences a working regime in the range of 33–45 °C, depending on Cr content, indicating the suitability of using the Fe-Cr-Nb-B powders for hyperthermia applications.