Study Of Character Of Electromagnetism Of Multilayers

Magnetic material which play an more and more important role in our modern lives has penetrated into virous industries of high technique. A bulk magnetic material will form magnetic film when its one demension becomes very small, and its magnetism changes to some extent. In the middle of 80's,people found that there existed coupling effect in multilayers of single crystle such as Y/Gd,Y/Dy. In 1988, French Baibich etc found magnetoelectric resistance (MR) whose value can reach 60% in Fe/Cr metal multilayers,they call it GMR. They thought it had some relation with coupling between layers at that time, but later people found the mechanism of GMR was different with anisotropic magnetoelectric resistance effect, it involved with spin dependent electron transporting process. We only need consider electron as carrier of electric charge in former electron transporting process, but in GMR effect ,electron not only is the carrier of electric charge, but also has spin. Spin tropism relative to regional magnetization vector will affect its transporting property. The discovery of GMR effect pioneered the new subject which is called magnetoelectronics.The GMR effect has became a international researching hotspot after the discovery of GMR effect of Fe/Cr multilayers. People found that multilayers formed by ferromagnetic metal of transition family and nonmagnetic metal or by alloy film and nonmagnetic metal will take on GMR effect. The value of GMR of Co/Cu multilayers is the biggest which can reach 65% under room temperature . GMR effect is also discoveried in guanular film,tunneling junction resistance and spin valve. Themagnetic head developed by IBM company with GMR effect increase the disk memory density 17 times which can reach 5Gb/in2 in the sixth year since GMR effect was discoveried. The memorizing density in lab now can reach 100Gb/in2 which keep it ahead in the competition with CD. GMR effect also can be applied in sensor and MRAM,so it brings broad attention. The MR of tunneling junction is the most attractive among these several GMR effects. It has large value because its saturated magnetic field is relatively low and its response to the change of magnetic field is relatively sensitive ,while the saturated magnetic field of the other GMR effect is too large. So TMR effect keeps ahead in the competition with other GMR effect. But there are few reports in these area, its electromagnetic characters are explored in this dissertation.