Magnetic-field-induced domain-wall motion in permalloy nanowires with modified Gilbert damping

Abstract

Domain wall ͑DW͒ depinning and motion in the viscous regime induced by magnetic fields, are investigated in planar permalloy nanowires in which the Gilbert damping ␣ is tuned in the range 0.008-0.26 by doping with Ho. Real time, spatially resolved magneto-optic Kerr effect measurements yield depinning field distributions and DW mobilities. Depinning occurs at discrete values of the field which are correlated with different metastable DW states and changed by the doping. For ␣ Ͻ 0.033, the DW mobilities are smaller than expected while for ␣ Ն 0.033, there is agreement between the measured DW mobilities and those predicted by the standard one-dimensional model of field-induced DW motion. Micromagnetic simulations indicate that this is because as ␣ increases, the DW spin structure becomes increasingly rigid. Only when the damping is large can the DW be approximated as a pointlike quasiparticle that exhibits the simple translational motion predicted in the viscous regime. When the damping is small, the DW spin structure undergoes periodic distortions that lead to a velocity reduction. We therefore show that Ho doping of permalloy nanowires enables engineering of the DW depinning and mobility, as well as the extent of the viscous regime.

Spin-orbit interaction enhancement in permalloy thin films by Pt doping

“…The magnetic films were deposited by cosputtering using Py and Py 90 Pt 10 10 compositions have been sputtered directly onto thermally oxidized silicon substrates. Because of the cosputtering method, the relative uncertainties in the film stoichiometries are small.…”

“…The other way to enhance the SOI in the ferromagnet is to dope it with a heavy element, as has been demonstrated in doped magnetic semiconductors [5]. Since the SOI affects a vast number of magnetic properties, many of which are important for various nanomagnetic or spintronic technologies, it would be convenient to tailor its strength and observe its impact on properties such as anisotropic magnetoresistance (AMR) [6], anomalous Hall effect (AHE) [7], magnetization damping phenomena [8,9], or different contributions to the torque acting on a magnetic domain wall by a field [10] or a spin-polarized current [11].…”

Local control of magnetic damping in ferromagnetic/non-magnetic bilayers by interfacial intermixing induced by focused ion-beam irradiation

“…The damping coefficient can be modified by introducing doping elements including rare earths [4][5][6][7] or transition metal 8,9 elements, with the dopant introduced by co-deposition, usually co-sputtering. A disadvantage of this approach is that the entire material is doped.…”

The contribution of Diamond Light Source to the study of strongly correlated electron systems and complex magnetic structures

“…However, even though the non-adiabatic contribution to β was found to increase with vanadium doping, the current density required to depin a domain wall also increased due to concomitant changes in the spin-polarization and saturation magnetization of the nanowire [104]. The group of Kläui (Mainz) has studied domain wall motion in Ni 80 Fe 20 nanowires doped with Ho (figure 8) using PEEM on beamline I06 [105,106]. Ho doping resulted in substantial variation in α and the non-adiabatic part of β implying that the spin relaxation that results in the spin torque is affected by spin dissipation processes that cause viscous damping.…”