Interaction effects in Permalloy nanowire systems

Abstract

Two series of self-organized hexagonal arrays of uniaxial Permalloy nanowires are grown by electroplating, filling of nanopores in anodic alumina films. Nanowires with periodicities of 65 and 105nm and wire diameter of 25–60nm were investigated by magnetization and ferromagnetic resonance (FMR) measurements. The length of the wires is 2.5μm, the volume ratio 0.13⩽v⩽0.43. A crossover transition from a one-dimensional easy axis “wire” behavior of weakly interacting uniaxial nanowires to a two-dimensional behavior of strongly coupled “wire film” having an easy plane anisotropy is determined from FMR measurements. The crossover occurs at v=0.27 for 105nm periodicity, and v=0.43 for 65nm periodicity. The system of the thinnest nanowires corresponds to a statistical ensemble of weakly interacting uniaxial particles, characterized by the highest coercivity of 1276Oe, the highest switching field distribution, and highest FMR linewidth, resulting from the broad distribution of individual wires. The coercivity monotonously decreases to 440Oe with increasing nanowire radius and volume fraction, as the wire shape anisotropy is reduced and the array anisotropy takes over due to dipolar interwire interaction, smoothing out the individuality of the wires. The behavior of coercivity, switching field distribution, and FMR linewidth is in accordance with the increase of the coupling of the nanowires.

Configurational spin reorientation phase transition in magnetic nanowire arrays

“…calculations, for nanowire periodicity D470 nm the RPT is expected to occur at higher wire diameter, in accordance with the results in Ref. [3], where for D=105, 25 oR c o30 nm.…”

“…As the critical value of the array's demagnetizing factor is 2 3 at the critical radius R c = 20 nm, the RPT is expected to take place in between samples SU02 and SU03, because of interwire interaction. As shown in Table 1, the RPT is experimentally observed close to the array SU03 [3]. According to the Table 1).…”

“…Particularly, such a configurational RPT was observed in series of 25r2R r60-nm-diameter hexagonal array of L=2.5 mm long uniaxial permalloy nanowires, having a periodicity of D=65 nm [3]. The RPT was demonstrated from studies about angular dependence of the ferromagnetic resonance (FMR) spectra that reflects the symmetry of the magnetic system.…”

“…In the present work, we make use of the measurements previously reported on nanowire arrays [3]. Arrays of permalloy nanowires were grown on anodic alumina template exhibiting hexagonal symmetry arrangement (see Fig.…”

Electrochemical synthesis of magnetic nanowires with controlled geometry and magnetic anisotropy

“…As the Fe content increases, however, the average saturation magnetization value of each nanowire also increases, and the increase in the strength of the magnetostatic interactions among nanowires provokes an apparent reduction of the effective anisotropy along the nanowire axis, thus reducing both the longitudinal coercivity and reduced remanence (Pardavi-Horvath et al, 2008). .14 Room temperature hysteresis loops of Permalloy nanowire array with a 36-nm pore diameter and 5-mm length measured parallel (k, circles) and perpendicular (?, squares) to the nanowire axis (Salem et al, 2012).…”