| Budget Amount *help |
¥15,900,000 (Direct Cost: ¥15,900,000)
Fiscal Year 2006: ¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 2005: ¥13,900,000 (Direct Cost: ¥13,900,000)
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| Research Abstract |
We can promote magnetization reversal and magnetic domain wall motion by an application of electric current through magnetic nano-pillars and wires, since in such magnetic structures, the electric current is spin-polarized and transfers angular momentum. In the experiments up-to-now, however, the results that cannot be understood by simple theories have been obtained. One of examples of such results is a reduction of switching speed at elevated temperatures. Therefore, in this research, we have tried to inject spin-polarized current into high quality magnetic tunneling junctions with a single crystal tunneling barrier in which symmetry of tunneling wave functions are controlled and a nano-sized wires. Then, we have tried to investigate details of the spin dynamics that is driven by a spin-transfer.
First, we observed rectification effect that happened when we applied rf resonant current to a magnetic tunneling junction that is under a magnetic field with oblique angle to the easy axis o
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f the magnetic cell. By observing frequency dependence of the rectification effect, we investigated the spin-dynamics. As results of the experiments, we found that the observed dc spectra are scattered. This result means that the dynamics of the spin-injection is not well controlled even if the tunneling junctions show clear spin injection magnetization switching. Then we tried to obtain well controlled spectra thus dynamics by controlling sample shape, layer structure, dimensions, and thicknesses. And we found that thinner magnetic film and control of magnetic domain using external field are effective to obtain well controlled and coherent dynamics.
We have also investigated spin-dynamics in magnetic cells in exchange coupling with antiferromagnetic layer. Since exchange field applied by the exchange coupling thought to be uniform, we expect coherent dynamic in such cells. After several tryals, we have succeeded to observe a ferromagnetic resonance of the exchange coupled free layer and spin injection magnetic reversal of it. The switch, however, was not complete but intermediate states appeared.
We have also observed noise from tunneling junctions and found increase of the low frequency noise under large injection current. This result implied that a large current causes an extinction of the coherency of the system. Less
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