Impact of interface orientation on magnetic coupling in highly ordered systems: A case study of the low-indexedFe3O4/NiOinterfaces

Abstract

We investigated the influence of the interface orientation on the magnetic coupling for the ͑110͒, ͑001͒, and ͑111͒ interfaces of epitaxial NiO thin films on single-crystal Fe 3 O 4 . In our analysis, we combine magnetic x-ray spectroscopies with circularly and linearly polarized light, i.e., x-ray magnetic circular and linear dichroism ͑XMCD and XMLD͒. A full treatment of the anisotropic XMLD in single-crystalline materials backed by theoretical support allows for a reliable vectorial magnetometry. Both the ͑110͒ and the ͑111͒ interfaces produce collinear coupling, which at first glance contradicts Koon's theory, while at the ͑001͒ interface, a perpendicular ͑spin-flop͒ coupling between a ferrimagnet and an antiferromagnet is observed. Furthermore, we find a pronounced enhancement of the interfacial uncompensated magnetization for the ͑110͒ interface only, while for the two other interfaces this value is considerably lower. These apparent discrepancies are resolved in terms of a detailed consideration of exchange and magnetoelastic effects for the individual orientations. The results highlight the fundamental role of the crystalline interface orientation in magnetic coupling phenomena involving oxidic systems.

Exchange bias in self-organized nanopatterned Cr/Fe junctions

“…1-3 Among them, exchange bias ͑EB͒, a characteristic unidirectional anisotropy observed after field cooling ͑FC͒ the system through the Néel temperature of the AF, has been for decades attracting a tremendous amount of experimental and theoretical attention. 1,2,[4][5][6][7] Despite the efforts made, a comprehensive understanding of EB has yet to emerge. The reasons for such a lack of a general picture are multiple.…”

“…Early experimental works on EB have been performed on systems whose MAE or interface morphology were not sharply defined, thereby leaving many of the above issues with no definite answer, whereas experiments performed on AF-FM systems with tailored MAE and/or interfacial morphology/ structure are recently starting to positively contribute to clarifying these points. [7][8][9][10][11][12] In this paper we address the EB properties of ultrathin epitaxial nanopatterned Cr/Fe/Ag͑001͒ multilayers characterized by atomic-scale-engineered interface morphology. The surface of the Fe layer was nanopatterned by the ion sculpting technique 13 prior to the Cr growth to create nanometricsized crystalline ripples coherently aligned along the ͓100͔ Fe direction ͑see Fig.…”

Surface magnetism of NiO investigated by magnetic spectromicroscopies

“…The deviation from bulk spin structure and a continuous spin reorientation transition from in-plane to out-of-plane direction is also reported for the case of NiO(100) thin films 57 The determination of spin-axis orientation or AFM vectors from XMLD data is not trivial. This requires extensive consideration of the crystal field effect in XMLD 58,59,60,61,20 , which (so called anisotropic XMLD effect) was neglected until recently. The presence of homogeneously distributed nanosized AFM domains in the thin film system can now explain the suppression of anisotropic behaviour of the XMLD effects 53,54 .…”

Observation of Micro-Magnetic Structures by Synchrotron Radiation Photoelectron Emission Microscopy

“…Until very recently, the interpretation of XMLD based on the atomic model 31) has been considered to be valid; however this idea has now been refuted for the XMLD analysis. [34][35][36][37] We have to consider the theory including the crystal symmetry. 38) Details of the antiferromagnetic domain imaging using XMLD are described in Sect.…”

“…Instead, there have been several investigations of the domain structures of ferromagnetic (or ferrimagnetic) and antiferromagnetic NiO interfaces already reported. [34][35][36][90][91][92][93] In these studies, XMCDand XMLD-PEEMs have played important roles, because spin-orientations in outermost surfaces, interfaces, and substrates can be observed experimentally. This is the advantage of PEEM with X-ray excitation over other microscopic methods.…”