X-ray magnetic circular dichroism studies of (001)-oriented NiFe∕Mn100−xPtx exchange bilayers

Abstract

(001)-oriented Ni80Fe20∕Mn100−xPtx and Co90Fe10∕Mn100−xPtx epitaxial bilayers were prepared using the molecular beam epitaxy method. Their exchange anisotropies were measured using a torque magnetometer, while their interfacial Mn uncompensated moments were measured by means of x-ray magnetic circular dichroism. The bilayers exhibited both one- and fourfold components in their anisotropy torque curves, which are difficult to explain using a simple model assuming the coherent rotation of ferromagnetic (F) and antiferromagnetic (AF) spins. Uncompensated Mn moments were confirmed to exist in the Mn100−xPtx layer due to exchange coupling with the adjacent F layer, and the Mn moment of CoFe∕Mn100−xPtx was found to be larger than that of NiFe∕Mn100−xPtx. In order to understand the experimental results, we extended the Mauri et al. [J. Appl. Phys. 62, 3047 (1987)] domain wall model by assuming cubic anisotropy in the AF and four AF domains whose interfacial moments are oriented along the principal axis of (001)-oriented Mn–Pt. The model predicted the uncompensated AF moment resulting from the domain wall formed in the AF layer and well reproduced the coexistence of one- and fourfold anisotropies in the in-plane torque curves. The uncompensated moment and torque curve were found to be dependent on the ratio of F/AF interfacial exchange coupling and the AF domain wall energy. By changing the ratio, it was possible to reproduce exchange anisotropy for various systems, such as NiFe∕MnPt, NiFe∕MnIr, and CoFe∕MnPt.

Model of hybrid interfacial domain wall in ferromagnetic/antiferromagnetic bilayers

“…However, in the early model of Néel and Mauri, only a limiting case that a thin ferromagnetic layer coupled with a very thick antiferromagnetic layer and reasonably the interfacial domain wall in the antiferromagnetic side, has been considered. Later theoretical studies as well as experimental investigations [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] suggest that the interfacial domain wall may exist in either the antiferromagnetic or ferromagnetic layer depending on the layer thickness and the magnetic-field intensity. [25] Nevertheless, a systematic study of both the full/partial antiferromagnetic domain wall (AFDW) and ferromagnetic domain wall (FMDW) in the practical exchange-biased bilayers is lacking, particularly with the interfacial exchange coupling involved.…”

Thickness dependence of exchange anisotropy for (0 0 1) oriented Mn89Pt11/NiFe and Mn80Ir20/NiFe bilayers

“…1(b) and 2(b) which are well explained by the single spin model. On the other hand, for the Mn 89 Pt 11 /NiFe bilayers, the domain wall formed in Mn 89 Pt 11 layer may give rise to AF crystalline anisotropy in their in-plane torque curve [10]. In this case the 4-fold (cubic) anisotropy will survive even in bilayers having thick Mn 89 Pt 11 as shown in Fig.…”