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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...

Ferromagnetic Co35Fe65, Fe, Co, and Ni nanowires have high saturation magnetizations (Ms) and magnetic anisotropies, making them ideal for magnetic heating in an alternating magnetic field (AMF). Here, Au-tipped nanowires were coated with polyethylene glycol (PEG) and specific absorption rates (SAR) were measured in glycerol. SAR increased when using metals with increasing Ms (Co35Fe65 > Fe > Co > Ni), reaching 1610 ± 20 W/g metal at 1 mg metal/ml glycerol for Co35Fe65 nanowires using 190 kHz and 20 kA/m. Aligning these nanowires parallel to the AMF increased SAR up to 2010 W/g Co35Fe65. Next, Co35Fe65 nanowires were used to nanowarm vitrified VS55, a common cryoprotective agent (CPA). Nanowarming rates up to 1000 °C/min (5 mg Co35Fe65/ml VS55) were achieved, which is 20x faster than the critical warming rate (50°C/min) for VS55 and other common CPAs. Human dermal fibroblast cells exposed to VS55, and Co35Fe65 nanowire concentrations of 0, 1 and 2.5 mg Fe/ml all showed similar cell viability, indicating that the nanowires had minimal cytotoxicity. With the ability to provide rapid and uniform heating, ferromagnetic nanowires have excellent potential for nanowarming cryopreserved tissues.