Micromagnetics of magnetic chemical modulations in soft-magnetic cylindrical nanowires

TL;DR

This paper investigates how magnetic modulations in soft-magnetic nanowires cause magnetization curling, how this curling depends on modulation length, and how it can be controlled by current-induced Oersted fields.

Contribution

It provides a combined analytical, experimental, and simulation study of magnetization curling in magnetic nanowires with modulations, revealing control mechanisms via current.

Findings

Magnetization curls around the axis in modulated nanowires.

Curling angle saturates at a specific modulation length.

Oersted field can switch the curling circulation.

Abstract

We analyze the micromagnetics of short longitudinal modulations of a high-magnetization material in cylindrical nanowires made of a soft-magnetic material of lower magnetization such as permalloy, combining magnetic microscopy, analytical modeling, and micromagnetic simulations. The mismatch of magnetization induces curling of magnetization around the axis in the modulations, in an attempt to screen the interfacial magnetic charges. The curling angle increases with modulation length, until a plateau is reached with nearly full charge screening for a specific length scale~$\Delta_\mathrm{mod}$, larger than the dipolar exchange length of any of the two materials. The curling circulation can be switched by the Oersted field arising from a charge current with typical magnitude $10^{12} A/m^{2}$ for a diameter of $\sim$100 nm, and reaching a maximum for $\Delta_\mathrm{mod}$.