Unusual Magnetic Hysteresis and Transition between Vortex and Double Pole States Arising from Interlayer Coupling in Diamond-Shaped Nanostructures

Abstract

Controlling the magnetic ground states at the nanoscale is a longstanding basic research problem and an important issue in magnetic storage technologies. Here, we designed a nanostructured material that exhibits very unusual hysteresis loops due to a transition between vortex and double pole states. Arrays of 700 nm diamond-shaped nanodots consisting of Py(30 nm)/Ru(t Ru )/Py(30 nm) (Py, permalloy (Ni 80 Fe 20 )) trilayers were fabricated by interference lithography and e-beam evaporation. We show that varying the Ru interlayer spacer thickness (t Ru ) governs the interaction between the Py layers. We found this interaction mainly mediated by two mechanisms: magnetostatic interaction that favors antiparallel (antiferromagnetic, AFM) alignment of the Py layers and exchange interaction that oscillates between ferromagnetic (FM) and AFM couplings. For a certain range of Ru thicknesses, FM coupling dominates and forms magnetic vortices in the upper and lower Py layers. For Ru thicknesses at which AFM coupling dominates, the magnetic state in remanence is a double pole structure. Our results showed that the interlayer exchange coupling interaction remains finite even at 4 nm Ru thickness. The magnetic states in remanence, observed by magnetic force microscopy (MFM), are in good agreement with corresponding hysteresis loops obtained by the magneto-optic Kerr effect (MOKE) and micromagnetic simulations.

Spatially Resolving the Magnetic Configuration of Trilayer Submicrometer Disks with Vortex Chiral Asymmetry Using X-Ray Resonant Magnetic Scattering

“…Such a double-layer structure is actually chosen in sensors and memory units, such as in spin valves and magnetic tunnel junctions. However, the studies using magnets with more than one magnetic layer are scarce due to the more difficult characterization of the buried layers [8,16,17]. Most of the magnetic sensitive microscopies with submicron resolution are surface sensitive, such as magnetic force microscopy (MFM) [18][19][20][21] and photoemission electron microscopy (PEEM) [22].…”