Interfacial Spins in Exchange Biased Pairs
Abstract
Today's magnetic storage devices consist of magnetic multilayers that are magnetically coupled across their interface. While the interface itself is supposed to dominate the magnetic behavior of the entire system, the identification and characterization of its magnetic properties remains an experimental challenge. A prominent example is the loop shift (unidirectional anisotropy, exchange bias) and the coercivity increase (uniaxial anisotropy) found if a ferromagnet is coupled to an antiferromagnet. The exchange bias effect is utilized in magnetic data storage device to form a pinned magnetic reference layer. Although exchange bias was discovered over 40 years ago by Meiklejohn our understanding of its origin is still poor. We use dichroism x-ray absorption spectromicroscopy in a photoemission electron microscope to study the magnetic coupling between antiferromagnetic NiO(001) and ferromagnetic Co across its interface. We observe large (1-20 μm) antiferromagnetic domains at the surface of bare NiO(001) single crystals. Upon in situ deposition of thin ferromagnetic Co layers (1.5 nm) a reorientation of the antiferromagnetic axes takes place. The uniaxial anisotropy axes of the ferromagnet and the antiferromagnet are then aligned parallel domain by domain. In another experiment the role of uncompensated spins in exchange biased coupled has been investigated. Uncompensated spins are found to be produced at the interface either by chemical reaction (Co/NiO) or intermixing (Co/IrMn, Co/PtMn). Two kinds of uncompensated spins are detected. Spins that follow the external field and such that remain pinned. An imbalance between free and pinned interfacial moments as origin of the unidirectional anisotropy will be discussed in the talk [1] H. Ohldag, A. Scholl et al., Phys. Rev. Lett. 86(13), pp. 2878, 2001. [2] F. U. Hillebrecht, H. Ohldag et al., Phys. Rev. Lett. 86(15), pp. 3419, 2001. [3] H. Ohldag, A. Scholl et al., Phys. Rev. Lett. 87, art. no. 247201 (2001).
- Publication:
-
APS Meeting Abstracts
- Pub Date:
- March 2002
- Bibcode:
- 2002APS..CSS.B1003O