Nanomagnetismus von epitaktischen Fe(110)- und CrO 2 (100)-Strukturen im Hinblick auf potentielle spinelektronische Anwendungen
As a result of the continuously increasing demands on the information technology within the last years new concepts of data storage systems have been developed. The combination of electronic and magnetic properties within so called spinelectronic or magnetoelectronic devices plays a key role in this area of research and technology. With the development of magnetic random access memories and magnetic-field sensors based on submicron magnetic elements there is a great deal of interest in understanding and controlling the micromagnetism of such elements. Furthermore the performance of such devices can be drastically enhanced by high-spinpolarized ferromagnetic materials. In chapter 1 investigations of the nanomagnetism of submicron epitaxial Fe(110) elements are presented. Magnetic force microscopy (MFM) measurements in conjunction with micromagnetic simulations show that the reproducible generation of remanent single-domain states is suppressed by the imperfection of the elements edges or by magnetic or structural defects of the magnetic material.The preparation and characterization of thin epitaxial (100)-oriented chromium dioxide films are presented in chapter 2. Chromium dioxide belongs to the class of half-metallic ferromagnets that are – in addition to the ferromagnetic properties – characterized by a high degree of spin polarization. By using two different chemical vapour deposition techniques thin chromium dioxide films were epitaxially grown on titanium dioxide substrates. Solid chromium trioxide and liquid chromyl chloride were used as precursors for these processes. As a result of extensive characterization of the films properties via x-ray diffraction, atomic force and scanning tunneling microscopy, SQUID magnetometry, magnetooptical Kerr measurements, and spin resolved photoelectron spectroscopy, the surface roughness of the films has been drastically reduced. It is shown that the so prepared films exhibit a high spin polarization and a pronounced anisotropic magnetic behavior. In cooperation with the IBM Almaden Research Center in San Jose, California, tunneling magnetoresistance (TMR) structures (chromium dioxide/MgO/CoFe) were prepared that showed positive and negative TMR ratios of about 7%. Furthermore a detailed study of the domain configurations and the magnetization reversal in small chromium dioxide wires using MFM and magnetoresistance (MR) measurements is introduced. It is shown that the low temperature MR response is dominated by intergrain-tunneling MR, while at high temperatures it is superseded by the anisotropic MR. Notches artificially introduced into the submicron wires act as attractive pinning centres for magnetic domain walls. Room temperature experiments to demonstrate a domain wall motion induced by an electrical current pulse (spin torque effect) show that the chromium dioxide is heated up by the required current densities so that the Curie temperature is exceeded. Also at low temperatures the change of the magnetic behavior induced by short current pulses can be attributed to temperature depending nucleation and pinning/depinning potentials of magnetic domain walls.
info:eu-repo/classification/ddc/530, Physik, Ferromagnetismus, Magnetoelektronik, Spinelektronik, halbmetallischer Ferromagnet, magnetische Domänen, magnetoelectronic, spinelectronic, halfmetallic ferromagnet, magnetic domains
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