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 15.145: Poster

Tuesday, March 27, 2007, 15:00–19:00, Poster A

Detection of superparamagnetic nanoparticles with AlOx magnetic tunnel junctions and development of hysteresis free MgO via shape anisotropy — •Sascha Walkenhorst, Michael Schilling, Simone Herth, Andreas Hütten, and Günter Reiss — Bielefeld University, Department of physics, Thin Films & Nanostructures, P.O. Box 100 131, 33501 Bielefeld, Germany

Signal enhancement was so far necessary for detection of single magnetic markers using magnetoresistive sensors. Detection without signal enhancement on basis of a magnetic tunnel junction (MTJ) would be an important feature for miniaturization and for applications as biosensors. Attempts based on conventional MTJs with AlOx and out-of-plane saturation of superparamagnetic beads were done. TMR measurements with and without beads on top of a sensor, alternatively saturated or not were compared. With Helmholtz-coils a shifted and narrow hysteresis is possible, whereas permanent magnets seem to be not applicable due to a very inhomogeneous field in this setup.

Elements are expected to have a hysteresis-free switching due to a perpendicular pinning. For MgO based sensors perpendicular pinning has been established via shape anisotropy. Arrays containing thousands of (sub-)micron elements were structured by electron beam lithography and ion beam etching. Measurements using the magneto optical Kerr-effect show a hysteresis free signal for low magnetic fields.