Spintronics i.e. spin based solid state devices, is an active field of research where the spin of an electron is utilized for logic or memory applications, with spin currents from a ferromagnet being used to perform the reading and writing operation [1-3]. Spin currents have also been shown to play an important role in the ultrafast manipulation of magnetization via all optical switching [4-6]. Hence, detailed understanding of spin currents from a ferromagnet to a non-magnet is a crucial step in the development of spintronic devices. However, directly observing these spin currents is extremely challenging due to the magnetic moment injected into non-magnet being very small, less than 1/10000 of a regular ferromagnet [7, 8]. We have developed an extremely sensitive spectro-microscopy detection method based on element specific x-ray magnetic circular dichroism, where current pulses driving the spin currents into the Cu layer are synchronized with the x-ray photons from SSRL. We have also implemented a normalization scheme where x-ray bunches in an even ring cycle (~780 ns) are normalized using the following odd cycle, to minimalize the intensity variations over the data integration period. The sensitivity of this ‘lock-in’ technique has allowed us to detect the extremely small transient Cu magnetization. We observe two spin currents induced effect in the Cu layer. The first effect is the transiently induced magnetization which occurs in bulk of the Cu layer due to spin accumulation and has a magnitude of 0.00003 μB per atom. The second effect occurs at the Co/Cu interface where we observe a 10% increase or 0.004 μB per atom for the hybridized Cu atoms due to spin torque-alignment. Another striking conclusion is that the injected current uses a significant portion of its moment already at the interface, and only a certain fraction makes it through the bulk of the Cu.
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3. http://www.everspin.com/spinTorqueMRAM.php
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