CoNiO x Interface

1. W mF MPI Halle The Unsolved Origin Of: - Loop shift (UNIDIRECTIONAL anisotropy) - - Loop widening (UNIAXIAL anisotropy) - If a ferromagnet is coupled to an antiferromagnet Giant Magneto Resistance: (GMR)-read headfor hard disks Co MCD Line shape in x-ray absorption used to identify metal-oxide transition: MMxOy “Real System” Co/NiO  Co/CoNiOx/NiO FM 1 FM 2 AFM 5mm NiO MCD Co Co CoNiO NiO NiO The Solution: PEEM to image AFM domains only at NiO(001) surface. SURFACE WALLS ARE NOT MIRROR PLANES LIKE BULK WALLS X-ray absorption shows chemically active interface PEEM reveals its polarization. Co DEPOSITION CREATES AND POLARIZES CoNiOX INTERFACE Chemical and magnetic characterization of all layers and their interface. The Method: Free Interfacial moments: - Exchange coupling - Uniaxial anisotropy - Coercivity increase A Photoemission Electron Microscope (PEEM) magnifies the local electron yield onto a screen. Spatial resolution ~ 50-100nm e o 30 Absorption of monochromatic tuneable x-rays elemental andchemical contrast Pinned Interfacial moments: - Exchange bias - Unidirectional anisotropy - Loop shift e- e- Fe2+ Ni Fe e- e- FeO Fe PEEM to image AFM andFM domains in Co/ NiO(001) AFM REORIENTATION UPON Co DEPOSITION PARALLEL COUPLING UNIAXIAL ANISOTROPY Fe3+ e- e- no Fe Absorption of circular polarized x-rays (circular dichroism)  spin orientation / ferromagnetic (FM) contrast XAS and dichroism  link between interface polarization and magnetic properties “FREE” CoNiOx SPINS CAUSE UNIAXIAL ANISOTROPY (EXCHANGE COUPLING) “PINNED” CoNiOx SPINS MAY CAUSE UNIDIRECTIONAL ANISOTROPY (EXCHANGE BIAS) e- e- Absorption of linear polarized x-rays (linear dichroism)  spin anisotropy / antiferromagnetic (AFM) contrast Interfacial Moments In Co/NiO Origins Of Antiferromagnetic/Ferromagnetic Coupling Hendrik Ohldag, Tom Regan, Andreas Scholl, Frithjof Nolting, Elke Arenholz, Franz Ulrich Hillebrecht and Joachim Stöhr Co And NiO CoNiOx Interface H. Ohldag, A. Scholl et al., Phys. Rev. Lett. 86(13), pp 2878 (2001). F.U. Hillebrecht, H. Ohldag et al., Phys. Rev. Lett. 86(15), pp 3419 (2001). H. Ohldag, N.B. Weber et al., Synch. Rad. News 13(6), pp. 25 (2001). T.J. Regan, H. Ohldag et al., Phys. Rev. B, in print (2001). Or on the web: http://www-als.lbl.gov/als/als_news/news_archive/vol.178_060601.html References