Giant magnetoreactance in magnetic nanowires

Abstract

We outline the idea of magnetic-field sensing with a nanometer spatial resolution using the effect of giant magnetoreactance (GMX) and we discuss results of our micromagnetic studies of domain-wall-assisted (or double-vortex-assisted) GMX in nanomagnets. By analogy to low-frequency giant magnetoimpedance (GMI), we consider systems of domains magnetized perpendicular to the direction of the AC current that creates an alternating Oersted field, thus, it drives the DW oscillations. Because of small cross-sections, the nanomagnets are not capable to induce large changes of the magnetic flux, therefore, the impedance of magnet-containing nanocircuits is dominated by the static resistivity (in accessible frequency regimes), while, GMX is an alternative effect to be utilized for sensing. We analyze in detail the effect in single-crystalline nanowire of cobalt with the easy axis transverse to the nanowire axis. In that system, small coherent shifts of the domain walls (DWs) induce relatively high changes of the magnetic flux through the largest cross-section of the nanowire due to large density of periodically packed DWs. Driven by the alternating transverse field of the Oersted origin, the system allows for perpendicular (the field directed perpendicular to the long axis of the nanowire and to the domain magnetization) GMX of improved characteristics (the GMX ratio and the field sensitivity of GMX) at a high stability of the magnetic structure in a wide region of the external field. Moreover, due to a non-zero overall magnetization (created by DWs), the perpendicular GMX is strongly asymmetric with respect to the field reversal (in a low-field regime). Also, we study the transverse GMX (the field parallel to the domain magnetization).