Study Of The Magnetic Sandwich And Its Application Characteristics For MRAM Devices

An electron is the carrier of both "charge" and "spin". With the dawn of the new millennium has emerged a novel technology which exploits electron spin and uses it to differentiate electrical carriers into two different types according to their spin directions. As the spin-electronics (spintronics) devices such as magnetic hard disk drive (HDD), spin transistor and magnetic random access memory (MRAM) were commercial used or developed as prototypes, spintronics becomes one of the most rapidly expanding fields in basic research and industrial application.MRAM has the advantages of nonvolatility, fast write and read times and low power consumption, and is potentially to be the memory standard. Magnetic sandwich with two ferromagnetic layers (FM) separated by a nonferromangtic layer (NM), is the key element of MRAM. When magnetic sandwich scales down to micrometer or sub-micrometer for the purpose of increase the recording density, its application characteristics changes profoundly. These includes: (a) The internal demagnetizing-field and magnetostatic coupling between magnetic layers increase significantly, which affect the transport properties of spin electrons; (b) The stability of the domains structure and the reversal characteristics of the memory cell will be worsen. In additional, the roughness and atomic interdiffusion between the layers will also cripple the GMR effect and application characteristics.In this thesis, the basic physical mechanisms of the aforementioned issues have been firstly analyzed. Then basic theory, experimental simulation, new materials and technologies have been explored and investigated based on the magnetic sandwich.Following are the main results:(1) The Camely-Barnas phenomenological theory is extended to study the magnetic sandwiches. The effects of interfacial spin-dependent-scattering-asymmetrical factor (Ns), and the electronic-mean-free path (X) on GMR ratio are calculated. The results show that large Ns and small X are helpful to obtain large GMR with thinner thickness of FM. Therefore, the Co-basis amorphous soft-magnetic films, which possess high spin polarization and short X, can be use to spin-valve sandwich to obtain larger GMR with small thickness.(2) The reversal processes of single magnetic dots and MRAM cell have been studied with finite element micromagnetic simulations. The simulation results of magnetic dots agree with the experimental results very well thus confirms the reliability and effectiveness of micromagnetic method. Under the nonuniform magnetic field...