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Electron microscope image of a magnetic nano wire with electric contacts

Ultra fast time resolved magneto transport

Working Group 2.52

In Fig. 1 the principle of our time resolved magneto transport setup is sketched. To detect the picosecond magnetization dynamics of a magnetic memory cell the cell is embedded into a coplanar wave guide (sense line). A magnetic field pulse is generated by a second coplanar wave guide (pulse line) on chip. Injection of a fast rising current pulse through the pulse line generates a fast rising magnetic field pulse at the magnetic memory cell. The pulse shape is monitored using a first channel of a fast sampling oscilloscope connected to the pulse line.

The magnetization dynamics of the magnetic memory cell can be detected using the so-called tunnelling magneto resistance (TMR). To measure the magnetization dynamics upon pulse application the cell is biased by a DC current. A magnetization motion induces a rapid change of the magneto resistance which in turn is detected via the signal line using the second channel of the fast sampling oscilloscope.

Fig 1: Sketch of the time resolved magneto transport setup.

A typical time resolved TMR-measurement of a memory cell is shown in Fig. 2. (a) shows the excitation pulse of 36 Oe amplitude and 81 ps duration.

The pulse induces a strong precession of the magnetization which is found in the magneto resistance oscillations shown in (b). The magnetization undergoes a damped precession at a frequency of 4.45 GHz. A Gilbert damping parameter of a = 0.02 is derived from comparison of the measured precession to simulations.

Fig 2: Precession of the magnetization of a magnetic tunnel junction cell. (a) magnetic field pulse. (b) time resolved precession of the magnetization of the cell.