Magnetic Heterostructures The Effect of Compositional Modulation on Magnetic Properties

Sammanfattning: The effect of compositional modulation on structural and magnetic properties of magnetic heterostructures was explored. The systems under focus were ferromagnetic superlattices Fe81Ni19/Co, metal-insulator multilayers Al2O3/Ni81Fe19, nanoparticles and artificial multilayered pillars.The heterostuctures were grown by magnetron sputtering in a state-of-the-art ultra-high vacuum system. The structural characterization was done by X-ray diffraction and reflectivity, as well as by transmission electron microscopy. Magneto-optical Kerr effect, SQUID and XMCD magnetometry and magnetic force microscopy were used for magnetic characterization.The bilayer thickness, ratio of the constituents and the interface quality influence the magnetic properties (magnetic moments and anisotropy) of metallic heterostructures. In particular, magnetic moments in bcc Fe81Ni19/Co superlattices were found to scale with the interface density thus, implying different magnetic moments at the interfaces as compared to the interior part of the layers. The easy direction of magnetization can be rotated from in-plane to out-of-plane, by increasing the bilayer thicknesses, keeping other parameters unchanged. Consequently, the anisotropy strength is strongly dependent on the repeat distance. Stripe domains appear in the films that possess an out-of-plane magnetization. The average domain period was found to be dependent on the applied in-plane magnetic field and on the total thickness of the films.The structural and magnetic properties of Al2O3/Ni81Fe19 multilayers depend strongly on the individual layers thicknesses. By increasing the amount of the magnetic deposits one can change the obtained film structure, from superparamagnetic nanoparticles to ferromagnetic multilayers. By increasing the oxide layer thickness the magnetic behavior of the nanoparticles can be altered from ferromagnetic, via spin glass like, to a superparamagnetic character.