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▲ [15p-501-18] Spin rotation of spin polarized currents in weak ferromagnets
Keywords:spin rotator, Spin-Hall effect, Perpendicular magnetized MTJ
It is of great interest to understand the change of spin polarization during the propagation of electrons. Spin polarized current is used in nano devices as a tool for magnetization switching. This switching is the basis for writing on memory devices, i.e. the usual Magnetic Tunnel Junction (MTJ), where the spin polarization is parallel or anti-parallel to the pinned layer’s magnetic moment. Spin polarized current injected into an MTJ by means of the spin Hall e ect is always in the in-plane direction, while it is known that a perpendicular direction is desired due to scalability.[1] The main question is: can this spin polarized current be changed in an arbitrary direction and thus in-plane injected current can be rotated into a perpendicular one, which makes usage in a perpendicular MTJ possible? This is important since the spin Hall e ect produces a higher spin polarized current than other methods of injection.
The in-plane oriented spin direction of electrons injected into an MTJ could be manipulated to a perpendicular orientation by the introduction of a ’spin rotator’. Our model makes use of a thin layer of a weak ferromagnet, such as Nickel, to take the role of the spin rotator. A weak ferromagnet is a ferromagnet with a small exchange splitting at the Fermi level.
A simple case has been studied where a spin polarized current is injected by means of the spin Hall e ect into the spin rotator with a magnetization perpendicular to both the polarization and direction of the current. The polarization as a function of thickness of the spin rotator has been calculated.
The polarization of the current does not align with the spin rotator immediately. Instead, the analytical results of this theory show that the spin precesses around the magnetization axis and only aligns gradually. It can therefore be seen as a damped harmonic oscillator, where the origin of the dampening can be found in elastic scattering with the spin rotator. A more realistic numerical calculation where we have integrated over the Brillouin zone to include all possible k-values is also done. This integration shows that there is an interference between the di erent wave vectors. Though it is not completely destructive, the polarization intensity reduces very strongly during the first rotation.
The in-plane oriented spin direction of electrons injected into an MTJ could be manipulated to a perpendicular orientation by the introduction of a ’spin rotator’. Our model makes use of a thin layer of a weak ferromagnet, such as Nickel, to take the role of the spin rotator. A weak ferromagnet is a ferromagnet with a small exchange splitting at the Fermi level.
A simple case has been studied where a spin polarized current is injected by means of the spin Hall e ect into the spin rotator with a magnetization perpendicular to both the polarization and direction of the current. The polarization as a function of thickness of the spin rotator has been calculated.
The polarization of the current does not align with the spin rotator immediately. Instead, the analytical results of this theory show that the spin precesses around the magnetization axis and only aligns gradually. It can therefore be seen as a damped harmonic oscillator, where the origin of the dampening can be found in elastic scattering with the spin rotator. A more realistic numerical calculation where we have integrated over the Brillouin zone to include all possible k-values is also done. This integration shows that there is an interference between the di erent wave vectors. Though it is not completely destructive, the polarization intensity reduces very strongly during the first rotation.