We developed an ultrafast time-resolved magneto-optical (MO) imaging system with several millidegree resolution of light polarization angle, 100 fs time-resolution, and a micrometer spatial resolution. A CCD camera with about 10(6) pixels is used for detection and MO images with an absolute angle of the light polarization are acquired by the rotating analyzer method. By optimizing the analysis procedure with a least square method and the help of graphical processor units, this novel system significantly improves the speed for MO imaging, allowing to obtain a MO map of a sample within 15 s. To demonstrate the strength of the technique, we applied the method in a pump-and-probe experiment of all-optical switching in a GdFeCo sample in which we were able to detect temporal evolution of the MO images with sub-picosecond resolution.

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Magnetic properties of Fe3O4 and magnetic tunnel junctions with Fe3O4 bottom electrode have been investigated. Highly conductive V/Ru layers were used as an underlayer of the Fe3O4 films. The V/Ru/Fe3O4 on [110] out-of-plane oriented MgO single crystal substrate show an anisotropy and high squareness along [11̄0] direction, while the Fe3O4 films with an underlayer of just Ru show isotropic behavior and low squareness. X-ray diffraction shows tensile stress on Fe3O4 for V/Ru/Fe3O4 samples. The anisotropy was shown to be induced by the stress. Finally, magnetic tunnel junction stacks of MgO/V/Ru/Fe3O4/AlO/CoFe/NiFe/Ru were deposited and the magnetic tunnel junctions with a junction size ranging from 2×2 μm2 to 9×9 μm2 were fabricated by optical lithography. The junctions show magnetoresistance ratios of ∼14% and no geometrical effect due to the junction size.

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Articles you may be interested inThe effect of film and interface structure on the transport properties of Heusler based current-perpendicular-toplane spin valves Layer thickness effect on the magnetoresistance of a current-perpendicular-to-plane spin valve

Magnetization switching of a relatively thick (9 nm) Gd-Fe free layer was achieved with a low spin injection current density of 1.0 × 106 A/cm2 using MgO based magnetic tunnel junction devices, fabricated for light modulators. At about 560 × 560 nm2 in size, the devices exhibited a tunneling magnetoresistance ratio of 7%. This low-current switching is mainly attributed to thermally assisted spin-transfer switching in consequence of its thermal magnetic behavior arising from Joule heating.

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