Swingback in magnetization reversal in MnAs–GaAs coaxial nanowire heterostructures

Abstract

The reversal processes of magnetization in epitaxial MnAs nanotubes prepared by anovergrowth on the sidewall of GaAs nanowires having a diameter of 26 nm are investigated.While the magnetic hard axis is aligned in the direction of the nanowire axis, we apply anexternal magnetic field perpendicular to the axis to examine the flipping characteristicsof magnetic moments. We determine the contributions from the substrate bya direct measurement in order to extract the magnetization of the core–shellheterostructures. The abrupt change in the thus-obtained magnetization due to a flipwhen the field is varied exhibits an overshoot at about 0.4 kOe for samples with athickness of the ferromagnetic shell (40–50 nm) larger than the diameter of the core.Moreover, the peak value exceeds the value when the field is swept in the oppositedirection. The magnetic hysteresis loop consequently involves line crossings. Wespeculate that the spin textures of domain walls in such thick hollow cylindersand their movement at the magnetization flip are affected by the geometry andmagnetostatic interactions of various origins, giving rise to the anomalous behaviour.