Ferromagnetic resonance in low interacting permalloy nanowire arrays

Abstract

Dipolar interactions on magnetic nanowire arrays have been investigated by various techniques. One of the most powerful techniques is the ferromagnetic resonance spectroscopy, because the resonance field depends directly on the anisotropy field strength and its frequency dependence. In order to evaluate the influence of magnetostatic dipolar interactions among ferromagnetic nanowire arrays, several densely packed hexagonal arrays of NiFe nanowires have been prepared by electrochemical deposition filling self-ordered nanopores of alumina membranes with different pore sizes but keeping the same interpore distance. Nanowires’ diameter was changed from 90 to 160 nm, while the lattice parameter was fixed to 300 nm, which was achieved by carefully reducing the pore diameter by means of Atomic Layer Deposition of conformal Al2O3 layers on the nanoporous alumina templates. Field and frequency dependence of ferromagnetic resonance have been studied in order to obtain the dispersion diagram which gives information about anisotropy, damping factor, and gyromagnetic ratio. The relationship between resonance frequency and magnetic field can be explained by the roles played by the shape anisotropy and dipolar interactions among the ferromagnetic nanowires.

Ni-Co Alloy and Multisegmented Ni/Co Nanowire Arrays Modulated in Composition: Structural Characterization and Magnetic Properties

“…The small tilting of the loops that is more evident for the Co NWs (larger saturation magnetization), is attributed to the inter-nanowire magnetostatic interactions [49][50][51][52] and explains the lower value of mr for Co NWs. In contrast, in the perpendicular configuration one detects narrow hysteresis loops with small HC and remanence magnetization, as theoretically expected [48].…”

Effect of Sharp Diameter Geometrical Modulation on the Magnetization Reversal of Bi-Segmented FeNi Nanowires

“…The deposition of the FeNi alloy nanowires was performed by using the diameter-modulated nanoporous alumina membranes, employed as templates, in a three-electrode setup suited with an Ag/AgCl reference electrode and Pt counter-electrode. An aqueous solution of NiSO 4 (90 g/L), FeSO 4 (14 g/L), ascorbic acid (1 g/L), and boric acid (25 g/L) was employed as the electrolyte [ 45 ]. A DC voltage of −1.4 V vs. the reference electrode was applied to the working electrode, resulting in the complete filling of the narrow segment and the partial filling of the wider one in a controlled manner ( Figure 1 e).…”

Effect of Sharp Diameter Geometrical Modulation on the Magnetization Reversal of bi-Segmented FeNi Nanowires

“…However, the coercive field of such interacting nanowire arrays underestimates the mean switching field of the nanowires in a proportion that depends on the interaction strength [45]. The extreme situation can be observed in the hysteresis loop of sample W2 where the strength of magnetostatic interaction is expected to be 5 times higher as a consequence of the large diameter of the nanowires for the same interpore distance [37,46,47]. Under the effect of the demagnetizing field due to the magnetostatic interactions, the antiparallel coupling of the NW in densely packed arrays would show zero net remanence of magnetization and thus anhysteretic behavior, as evidenced in the hysteresis loop of W2 sample.…”

“…The deposition of the FeNi alloy nanowires was performed by using the diameter modulated nanoporous alumina membranes, employed as templates, in a three-electrode setup suited with an Ag/AgCl reference electrode and Pt counter-electrode. An aqueous solution of NiSO4 (90 g/l), FeSO4 (14 g/l), ascorbic acid (1 g/l) and boric acid (25 g/l) was employed as electrolyte [37]. A dc voltage of -1.4 V vs reference electrode was applied to the working electrode, resulting in the complete filling of the narrow segment and the partial filling of the wider one in a controlled manner (Figure 1e controlling the deposition time in the range between and s it has been possible to synthesize two different FeNi diameter modulated nanowire array samples with varying length of the wide segment.…”