SPring-8, the large synchrotron radiation facility

Date : 15:00-  October  25

Place : Auditorium in the central building

Speaker : Dr.Claus  M. Schneider

Affiliate : Research Centre Julich

Title : Interface Magnetism in Spintronics Model Systems

Abstract :

Spintronics devices are often composed of complex layer stacks. The magnetic and magnetotransport properties of these layered systems are determined not only by the characteristics of the individual layers, but even more so by the interfaces between them. Magnetic coupling phenomena and spin-dependent transport are sensitively affected by the atomic arrangement and magnetic nanostructure at the interfaces. We have therefore studied the interface magnetism in two spintronic model systems: MgO/Fe(001) and NiO/Fe₃O₄(011).

The Fe/MgO system is well known for its high tunneling magnetoresistance effects [1,2], presumably caused by coherent tunneling through matched electronic states. Using spin-polarized photoemission spectroscopy, we have studied the spin-split electronic states in Fe(001) upon deposition of ultrathin MgO films of variable stoichiometry [3]. Whereas for stoichiometric MgO overlayers the Fe spin polarization remains unchanged,
overoxidation of the Mg leads to a clear reduction of the Fe spin polarization, caused by the formation of interfacial FeO. An oxygen deficiency in the MgO layer, however, causes a significant increase of the
Fe spin polarization, which may be explained through the electronic interaction with O vacancies.

The interface between antiferromagnets (AF) and ferromagnets (FM) gives rise to the phenomenon of exchange bias, which is often used to define a magnetic reference in spintronics. The combination NiO (AF) and Fe₃O₄ (FM) constitutes an interesting model system, as oxidic interfaces promise higher structural and magnetic quality than metallic ones. In our studies we addressed the magnetic coupling of ultrathin NiO overlayers on Fe₃O₄ single crystal surfaces by means of soft x-ray photoemission microscopy. By exploiting circular (XMCD) and linear (XMLD) magnetodichroic contrast mechanisms, we find clear evidence for a spin-flip coupling between AF and FM along the (011) direction (see figure), which may be mediated through the superexchange interaction across the interface. In addition, we observe a proximity effect on the NiO-side of the interface, leading to a sizable ferromagnetic response of the interfacial NiO layer. A similar behavior is found for the (111) axis, whereas the (001) axis behaves differently.

Organizer : KINOSHITA (PHS 3129)