Magnetic viscosity in iron-rhodium nanowires

Noble/transition bimetallic nanowires of nominal composition Fe90Rh10 are AC electrodeposited into 20 nm diameter hexagonally self-assembled alumina nanopores. Nanowires about 18 nm in diameter and 1 mu m long are polycrystalline and multiphase. Wires contain alpha-Fe grains and very small grains of the ClCs-type alpha'-Fe(Rh) phase. The room temperature magnetization mechanism and the thermal stability of nanowire magnetic configurations are further investigated by measuring the dependence of the coercive field on the applied field sweeping rate R. From these data a mean fluctuations field value of mu H-0(FR) = (9.0 +/- 0.5) mT is obtained (at coercivity) and an effective activation magnetic moment mu(ac) = 5400 mu(B) is estimated, with mu(B) the Bohr magneton. At the coercive field (about 45 mT) the resulting activation lengths become l(AC) approximate to 6.4 and 6.7 nm for alpha-Fe and alpha'-Fe(Rh), respectively. Assuming an effective magnetic anisotropy, considering magnetostatic shape contributions in addition to the magneto-crystalline one, the domain wall thickness delta(w) in alpha-Fe grains and in the alpha'-Fe(Rh) become delta(wFe) = 13.4 nm and delta(wFeRh) = 10.9 nm respectively. These values are comparable to the activation lengths estimated at the coercive field in each phase. These facts strongly indicate that irreversible polarization reversal in these nanowires takes place by local curling, involving localized nucleation modes. (C) 2017 Elsevier B.V. All rights reserved.