Uncovering Magnetic Order in Nanostructured Disordered Materials A Study of Amorphous Magnetic Layered Structures

Detta är en avhandling från Uppsala : Uppsala Universitet

Sammanfattning: The scope of this thesis is the study of the interplay between structure and magnetism in amorphous materials. The investigations focus on the growth of amorphous layers and the study of the in?uence of structural disorder and reduced physical extension on the magnetic properties of thin ?lms and multilayers. The examined magnetic materials are FeZr alloys, as well as other amorphous transition metal alloys such as CoZr and FeCoZr.Thin ?lms and multilayers of the studied materials were deposited using magnetron sputtering in ultra-high vacuum conditions. Their amorphous structure and layering quality was investigated using X-ray scattering techniques and in several cases with transmission electron microscopy. The chemical composition of the alloys was determined with Rutherford Backscattering Spectrometry. The magnetic properties were investigated using the magneto-optic Kerr effect and SQUID magnetometry, as well as polarized neutron re?ectometry and X-ray magnetic circular dicroism measurements.For FeZr alloys deposited as multilayers with Al2O3 as spacer layer, it was found that Fe-rich nanocrystallites, formed at the metal/oxide interfaces, exert large in?uence on the magnetic properties. The use of AlZr alloys as buffer layers promotes the growth of highly amorphous FeZr layers. FeZr/AlZr multilayers with good layering quality can also be obtained. The in?uence of the reduced layer thickness on the magnetic moment, Curie temperature and magnetic dimensionality of the magnetic layers is addressed for FeZr/AlZr multilayers. Thin FeZr layers in these structures are found to belong to the 2D XY dimensionality class. The change of the magnetic moment and Curie temperature with reduced FeZr layer thickness is quanti?ed.In addition, the induced magnetic moment in the alloy element Zr was investigated in FeZr and CoZr alloy ?lms. The possibility to imprint a preferred magnetization direction during thin ?lm preparation was demonstrated for FeCoZr layers. Lastly, AlZr alloy ?lms were studied with respect to their oxidation stability at room and elevated temperatures, aiming towards development of materials with passivating properties.