Py/Au/Py非區域自旋閥自旋電子擴散長度研究

Abstract

非區域自旋閥的磁電阻變化是目前熱門的研究主題，已經被廣泛應用在電腦硬碟的讀取頭上。我們樣品的結構是兩個鎳鐵合金夾著金的三明治結構(NiFe/Au/NiFe)，我們在一端NiFe(F1)加上電流源，另一端NiFe(F2)則接上電壓源量測，這種特殊的量測方法可以讓我們確定量測到的訊號是由自旋電流所造成的，當我們外加磁場極化鎳鐵合金時，當F1內的電子流入Au時在介面產生自旋電子不均勻累積，因為自旋向上和向下的電子數目不同，所以會造成Au內的自旋向上和向下的費米能階分裂，分裂的大小會隨著和F1的距離增加而減少，費米能階分裂在巨觀的表現就是電阻的差，因此最後當F2和F1平行時可以量到一個較大的電阻值，F2和F1反平行時可以量到一個較低的電阻值，這兩個電阻的差(∆R)就是我們的量測目標，我們藉由量測不同間距的樣品可以得到不同大小的∆R，參考多篇paper後我們假設NiFe的極化率是0.2，由此可以推算出自旋電子在我們的系統中擴散長度可以長達2.8μm

The magnetoresistance change of nonlocal spin valve is currently a hot research topic that has been widely used in the computer’s hard disk read heads. The geometry of our sample is that a non-magnetic Au film is connected by two ferromagnetic NiFe contacts. One NiFe electrode is spin-injector F1 and another is spin-detector F2. When spin polarization electrons inject from F1 into Au, and a non-equilibrium spin accumulation is induced in Au. The spin accumulation is manifested in the Au band structure as a splitting of the Fermi levels between spin-up and spin-down electrons. The detector is utilized to measure the spin accumulation. Depending on the relative orientations of the detector spin and the spin accumulation, a voltage contrast can be measured between F2 and Au. When F2 is aligned parallel to the spin accumulation, its Fermi level is aligned with the upper Fermi level in Au, and thus exhibits a high resistance. Otherwise a low resistance is measured. The resistance difference (∆R) is our goal to be measured. We can calculate the spin diffusion length when we know the ∆R. In my system, the max ∆R is 30mΩ and the max spin diffusion length is 2.8 micrometer.