Regensburg 2007 – scientific programme
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MA: Fachverband Magnetismus
MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)
MA 15.21: Poster
Tuesday, March 27, 2007, 15:00–19:00, Poster A
Spinresolved Photoemission Spectroscopy of Amorphous CoFeB — •Martin Sperlich1, Coen Smits1, Reza Gadhimi4, Frank Matthes2, Theodoros Dimopoulos3, Joachim Wecker3, Claus M. Schneider2, and Gernot Güntherodt1 — 1II. Physik. Inst., RWTH Aachen — 2Inst. für Festkörperforschung, FZ Jülich — 3Siemens AG, Corporate Technology — 4Gemeinschaftsinstitut für Elektronenmikroskopie, RWTH Aachen
Tunnel magnetoresistance (TMR) junctions of the system CoFeB/MgO/CoFeB based on amorphous CoFeB show the highest TMR values of all FM/MgO/FM junctions (FM = ferromagnet) of over 350% at room temperature [1]. This is very surprising since the highest TMR values have been theoretically predicted for epitaxial junctions. Due to annealing the TMR values increase which is attributed to a surface crystallisation of the amorphous CoFeB at the interface with MgO. By means of UV Spin-polarised Photoemission Spectroscopy (SP-PES) we have investigated the spin polarisation of amorphous CoFeB films. On a relative scale compared to tunneling the spin polarisation obtained from SP-PES gives an indication of the influence of annealing processes on the TMR values. Upon annealing at 275 °C the spin polarization of CoFeB increases by a factor of two. This is explained by the onset of surface crystallisation of CoFeB and a reduction of oxygen at its surface. We paid special attention to the metal/oxide interfaces by using Mg/MgO overlayers on CoFeB. The oxidation states of Mg were controlled by the position of the Mg 2p core levels. - [1] Y.M. Lee et al., Appl. Phys. Lett. 89, 042506 (2006)