Spin-dependent Transport Properties Of The Iron-based Magnetic Films

Different from the traditional microelectronic devices, spintronic devices employ spin on information storage, processing and transport, which have the advantage of nonvolatility, stability, high integration, low energy cost, and fast speed. So they have the potential application prospect in fields of the communication, the national defense, the aviation and spaceflight, etc..In all spintronic materials, iron-based spintronic material is the most striking and useful one. In this paper, three kinds of Fe-based spintronic materials are investigated theoretically and experimentally. Two types of physical issues are concerned. One is about the tunability of the physical properties of the half-metal. The other is about the origin and the application of the extraordinary Hall effect of the nanocrystalline magnetic films. The results are shown below.1. Polycrystalline Fe3O4 films are synthesized at room temperature. Annealing effects on the physical properties are investigated systematically. For the as-deposited film, the magnetoresistance (MR) value is about 9.1%, which is a considerable value comparing with the reported monolayer Fe3O4 films. By annealing it in vacuum, the grain size, the thickness of the boundary, the saturated magnetization and the resistivity of the films can all be tuned. After annealing it in air, a uniformγ-Fe2O3 layer formed on the grain surface, which acts as the tunneling barrier in the electron transport process. As a result, the tunneling energy increases, which will enhance the resistivity. The height and width of the barrier can easily be tuned. All results show that the resistivity can be tuned more than three orders at room temperature, and about seven orders with different temperatures, which can satisfy the needs of injecting the spin polarized current in the spintronic devices.2. Physical properties of polycrystalline Fe3-xZnxO4 and Fe3-xPtxO4 films are investigated theoretically and experimentally. First principle calculation on Fe3-xZnxO4 indicates that with increasing the Zn2+ concentration, the total magnetic moment (Mtot) increases firstly and then decreases, the carrier concentration decreases, the resistivity increases, and the half-metallic properties are kept. First principle calculation on Fe3-xPtxO4 indicates that the Mtot and the occupation of the t2g orbit decreases when doping Pt2+ on B sites. The experimental investigations indicate that the Pt ions are doped on B site. The conduction is controlled by tunneling. The saturated magnetization, the resistivity and the magnetoresistance decrease with increasing the Pt2+ concentration, while the spin polarization keeps a high value, consistent with the results of the first principle calculation. Relations between the Hall and longitude conductivity satisfyσxy∝σxxn for all samples, where n is between 1.72～1.57±0.02, in accordance with universal scaling theory.3. Physical properties of the nanocrystallineε-Fe3N films are investigated systematically. Microstructure, composition, magnetic properties and resistivity measurements show that all samples exhibit ferromagnetic properties at room temperature. The saturated magnetization and resistivity are stable with temperature. Samples with different amorphous compositions show diverse Hall effect, in which the sample containing little amorphous compositions fulfills the universal scaling theory between Hall and longitude resistivity. However, the universal scaling theory is invalid for the sample with a great many of amorphous compositions. The electrons relaxation time in amorphous layers has a tremendous effect on the extraordinary Hall effect. Besides, a new-style of Hall devices is developed, which has the advantage of the small size, low cost, high temperature and magnetic field stability, low resistivity and good linearity. So it is valuable in the spintronic devices application.