Magnetic domain texture and Dzyaloshinskii-Moriya interaction in systems with perpendicular exchange bias

We sputter-deposited polycrystalline multilayers of Pt/Co/IrMn and Pt/Co/FeMn exhibiting perpendicular exchange bias (PEB). These multilayers are of interest because of the coincidence of the Dzyaloshinskii-Moriya interaction (DMI) with a vertical exchange field that could remove the need for an externally applied field to stabilise skyrmions [1]. We measured the exchange bias as a function of the layer thickness of Co, IrMn, and FeMn.

Utilising Kerr microscopy and XMCD-PEEM imaging, the domain morphology of the ferromagnetic (FM) layer (Co) was studied when crossing over the paramagnet to antiferromagnet (AFM) phase transition of the coupled AFM layers (IrMn and FeMn). The domain texture is influenced by the FM-AFM exchange coupling. A domain created by nucleation has rough edges, while a domain cooled through the transition maintains its smooth appearance.

The DMI brings about chiral magnetic order, such as Néel domain walls and skyrmions. The DMI was investigated in these systems, particularly how it is affected by the AFM spin order. The DMI was measured at different phases of the AFM layers. We quantified the DMI by Brillouin light spectroscopy [2].

[1] Fert et al. Nat. Nano. 8, 152 (2013).
[2] J-H Moon et al. PRB 88, 184404 (2013).