Magnetic remanent states in antiferromagnetically coupled multilayers

TL;DR

This paper investigates the stable magnetic remanent states in antiferromagnetically coupled multilayers, revealing how topologically stable defects influence hysteresis and domain patterns through a phenomenological model and experimental validation.

Contribution

It introduces an analytical model for the equilibrium sizes of ferroband defects in multilayers, linking them to exchange interactions, magnetic fields, and geometry, and explains hysteresis phenomena.

Findings

Analytical expressions for ferroband sizes as functions of material parameters.

Phase diagram showing regions of different magnetic domain patterns.

Experimental validation with magnetic force microscopy images.

Abstract

In antiferromagnetically coupled multilayers with perpendicular anisotropy unusual multidomain textures can be stabilized due to a close competition between long-range demagnetization fields and short-range interlayer exchange coupling. In particular, the formation and evolution of specific topologically stable planar defects within the antiferromagnetic ground state, i.e. wall-like structures with a ferromagnetic configuration extended over a finite width, explain configurational hysteresis phenomena recently observed in [Co/Pt(Pd)]/Ru and [Co/Pt]/NiO multilayers. Within a phenomenological theory, we have analytically derived the equilibrium sizes of these "ferroband" defects as functions of the antiferromagnetic exchange, a bias magnetic field, and geometrical parameters of the multilayers. In the magnetic phase diagram, the existence region of the ferrobands mediates between the regions of patterns with sharp antiferromagnetic domain walls and regular arrays of ferromagnetic stripes. The theoretical results are supported by magnetic force microscopy images of the remanent states observed in [Co/Pt]/Ru.