Magnetization processes in electrodeposited NiFe/Cu multilayered nanowires
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na-Georgiana Dragos, Anca-Eugenia Moga, Nicoleta Lupu, and Horia Chiriac National Institute of Research and Development for Technical Physics, 700050 Iasi, Romania (Received 2 September 2010; accepted 15 February 2011)
The effect of the magnetic anisotropy and the dipolar interactions between NiFe magnetic layers and between nanowires on the magnetic properties of NiFe/Cu multilayered nanowire arrays electrodeposited into the nanopores of anodic aluminium oxide (AAO) templates with diameters of 35 and 200 nm has been studied. The variation of the aspect ratio (thickness/diameter) between the NiFe magnetic and Cu nonmagnetic layers influences the effective anisotropy field. The correlation between the measured hysteresis loops, with the applied field parallel and perpendicular to the multilayered nanowires’ axis, and the calculated effective anisotropy field, Heff, and saturation field, Hsat, shows that it is possible to tune the orientation of the magnetization axis with high accuracy. Two formulas, which include both the intra- and internanowire interactions, were proposed to calculate the saturation fields of multilayered nanowire arrays for the applied field parallel and perpendicular to the nanowires’ axis. I. INTRODUCTION
After the discovery of the giant magnetoresistance (GMR) effect1 and its use in high-density magnetic recording media2 and novel magnetic sensors,3,4 the interest for one dimensional and two dimensional magnetic materials showing a significant magnetoresistance (MR) response increased significantly. Recently, single and multilayered ferromagnetic nanowires have been prepared and studied both from the fundamental point of view and concerning their potential applications. Especially for multilayered nanowires, the interest has been boosted after the evidence of the GMR effect for current perpendicular to the plane configuration.5–7 Another very promising area of applications for multilayered nanowires derives from the pioneering work of Berger8 and Slonczewski.9 A spin-polarized current can transfer its angular momentum to a ferromagnet, inducing a torque on its magnetization. Thus, the magnetic moment can switch to another state or oscillate around its equilibrium position at microwave frequencies. These are known as the spin transfer torque (STT) phenomena. The potential applications of these phenomena are in nonvolatile memories10,11 and high-frequency telecommunications.12 There are many different ways to produce nanowires, including chemical vapor deposition,13 vapor–solid– liquid technique,14 and lithography technique.15 But one a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.62 J. Mater. Res., Vol. 26, No. 9, May 14, 2011
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of the cheapest ways is the electrochemical deposition.16 It is also a fast technique allowing to produce large arrays of identical magnetic entities with large aspect ratios (length divided by diameter), which is not possible with standard lithographic techniques. For st
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