The Study Of Structure And Character Of Ferromagnetic Tunnel Junction And Granular Films

In this thesis, we briefly introduces the study of magnetoresistance matter. The Fe/Al2O3Fe magnetic tunnel junction(MTJ) , Co/Al2O3/FeNi MTJ and a FexCu(1-x) granule film have been fabricated. We introduce the fabrication of all samples and anneal of FexCu(1-x) granular film in detail. The configuration of granule film is investigated by scanning tunneling microscope(STM).The matter phase is analyzed by X-ray diffraction (XRD).The hysteresis loop of Co/Al2O3/FeNi magnetic tunnel junction is studied by vibrating sample magnetometer(VSM). We use microresistance test system (MTS)to investigate the character of resistance , conductance , voltage and current. Lastly ,We use Ziman theory to explain the novel dependence of the resistivity on the injection current.The achievements are listed as follows: 1). Study on the fabricating methodThe Fe/Al2O3/Fe MTJ and Co/Al2O3/FeNi MTJ are prepared by ion-beam sputtering systems. The FexCu(1-x) granule films were evaporated directly using a high vacuum electron beam evaporation. Some samples of granule films are annealed at 340C. 2). Structure tokenThe XRD, STM are employed to find:(1) Plenty of grains are assembled at the surface. The average diameter of the grains is about 9.57nm.(2) The thicker of film, the higher of crystal degree. If the element is more than the other ,It is easier to be crystallized. Anneal make film easy to be crystallized too. At the same time a part of element is oxidated. 3). Characteristic investigationWe use VSM and MTS to study the main result as Follows:(1) The hysteresis loop of Co/Al2O3/FeNi MTJ is a typical two Hc loop.(2) We investigate the dependence of the conductance on voltage. We find that the curve is approximately horizontal beeline at low voltage ,but conic at high voltage.(3) The V-I character of Co/Al2O3/FeNi MTJ accord with Ohmic law when the current is under 10mA. It is not Ohmic when current is raised continuously. The junction voltage decreases with the increase of current above 10mA. There is an effect of the negative resistance. To fit the V-I cure with Simmons formula, we get that the effective height of the junction barrier is 2.5 eV and the effective breadth is 1.8 nm.(4) The p - I characteristic of FexCu(1-x) granule film is studied. The resistance test atmicro current can be not make sure. The same with normal metal film ,Fe0.3Cu0.7 (500nm) granular film have positive coefficient of temperature. The negative resistance is observed in FexCu(1-x) granular film under certain condition. This characteristic of negative resistance is weakened or changed to positive with the change of thickness of film, ratio of Fe atom to Cu atom, anneal, test temperature. 4). Theory discussAccording to Ziman theory , When 2KF is equal to Kp. non-crystal metal have negativecoefficient of temperature. Then the p - I characteristic of FexCu(1-x) granular film can be explained qualitatively.