Investigation Of Anomalous Hall Effect And Magnetic Skyrmion In Perpendicular Magnetic Thin Films

Recently, perpendicular magnetic nanostructures have been widely considered as promising candidates in future spintronics because of the excellent properties of perpendicular nanostructures. For example, a giant linear anomalous Hall effect in the MgO/CoFeB/Ta thin film has recently been found, which has made PMA magnetic thin film a potential candidate of magnetic sensor. More recently, it was reported that in magnetic thin films with PMA, there exist magnetic skyrmions. It is reported that magnetic skyrmions can be well stable at room temperature in perpendicular [Co/Pt]N multilayers.Although perpendicular magnetic nanostructures have been intensively studied, there still exist problems that have not been investigated. For example, the investigation of magnetic sensors based on anomalous Hall effect of perpendicular magnetic thin films under very low temperature is still lacking. On the other hand, although it is widely recognized that skyrmion based magnetic racetrack memory is promising in magnetic data storage, further investigation are still needed to be done to better understand the dynamics of magnetic skyrmions driven by current or spin waves in magnetic nanowire.This thesis mainly focused on the investigation of perpendicular magnetic nanostructures. Experimentally, magnetic thin films were grown by high vacuum magnetron sputtering system. We investigated weak localization correction to the anomalous Hall effect in MgO/CoFeB/Ta perpendicular thin films. Also, through micromagnetic simulation, we investigated the motion of magnetic skyrmions driven by current and spin waves in magnetic nanowires.Experimentally, CoFeB single layer films with thickness of 1.7 nm ~ 10.5 nm and MgO/CoFeB/Ta perpendicular thin films with CoFeB thickness of 0.8 nm ~ 1.4 nm were grown by magnetron sputtering. We then measured the electron transport properties of amorphous CoFeB and MgO/CoFeB/Ta thin films at low temperature. It is found that for amorphous CoFeB single layer, when CoFeB thickness is larger than 3 nm, the side jump mechanism dominates the anomalous Hall effect and the weak localization correction to anomalous Hall effect cannot be observed. For CoFe B thinner than 3 nm, however, both the side jump and skew scattering mechanism contributes to anomalous Hall effect and the weak localization correction is observable. On the other hand, for MgO/CoFeB/Ta perpendicular thin films, the weak localization is observable only when the sheet resistance of the sample is larger than 1.5 k?, due to the contribution of additional conduction channel provided by Ta layer in MgO/CoFeB/Ta perpendicular thin films.In addition, micromagnetic simulation was carried out to investigate the motion of magnetic skyrmions in perpendicular magnetic nanowires. It is found that the size of the skyrmion can be tuned not only by intrinsic magnetic parameters, but also by external magnetic field. Furthermore, the skyrmion velocity linearly depends on the size of the skyrmion. In the presence of the defects in the nanotrack, the depinning of skyrmions in the chain depends not only on the size of defect, but also on the repulsive skyrmion–skyrmion interaction. It is also found that propagating spin waves can drive the skyrmion into a stream motion. The velocity of the skyrmion motion is controlled by the changes of spin waves frequency, spin waves exciting field amplitude and the size of skyrmion.