Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers

TL;DR

This paper uses phenomenological theory to analyze magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers, revealing complex behaviors including multistate coexistence and inhomogeneous states influenced by anisotropy and applied fields.

Contribution

It provides a comprehensive survey of magnetic states and transitions in multilayer systems with even ferromagnetic layers, highlighting new complex inhomogeneous and metastable states.

Findings

Multistate coexistence regions in phase diagrams.

Inhomogeneous noncollinear magnetic states across multilayers.

Discontinuous transitions with transitional domain structures.

Abstract

In antiferromagnetically coupled superlattices grown on (001) faces of cubic substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or Fe/Cr, the magnetic states evolve under competing influence of bilinear and biquadratic exchange interactions, surface-enhanced four-fold in-plane anisotropy, and specific finite-size effects. Using phenomenological (micromagnetic) theory, a comprehensive survey of the magnetic states and reorientation transitions has been carried out for multilayer systems with even number of ferromagnetic sub-layers and magnetizations in the plane. In two-layer systems (N=2) the phase diagrams in dependence on components of the applied field in the plane include ``swallow-tail'' type regions of (metastable) multistate co-existence and a number of continuous and discontinuous reorientation transitions induced by radial and transversal components of the applied field. In multilayers (N \ge 4) noncollinear states are spatially inhomogeneous with magnetization varying across the multilayer stack. For weak four-fold anisotropy the magnetic states under influence of an applied field evolve by a complex continuous reorientation into the saturated state. At higher anisotropy they transform into various inhomogeneous and asymmetric structures. The discontinuous transitions between the magnetic states in these two-layers and multilayers are characterized by broad ranges of multi-phase coexistence of the (metastable) states and give rise to specific transitional domain structures.