“And the day came when the risk to remain tight in a bud was more painful than the risk it took to blossom.” Anais Nin (1903 - 1977) List of Papers This thesis is based on the following papers, which are referred to in the text by their Roman numerals. I Morphology of amorphous Fe91Zr9/Al2O3 multilayers: Dewetting and crystallization A. Liebig, P.T. Korelis, H. Lidbaum, G. Andersson, K. Leifer and B. Hjörvarsson, Phys. Rev. B 75, 214202 (2007) II Highly amorphous Fe90Zr10 thin films, and the influence of crystal- lites on the magnetism P.T. Korelis, A. Liebig, M. Björck, B. Hjörvarsson, H. Lidbaum, K. Leifer and A.R. Wildes, Thin Solid Films 519, 404-409 (2010) III Experimental realization of amorphous two-dimensional XY mag- nets A. Liebig, P.T. Korelis, Martina Ahlberg, and B. Hjörvarsson Phys. Rev. B 84, 024430 (2011) IV Magnetic and structural properties of amorphous Fe90Zr10/ Al75Zr25 multilayers in the two-dimensional limit P.T. Korelis, P.E. Jönson, A. Liebig, H.-E. Wannberg, P. Nordblad, and B. Hjörvarsson, To be submitted V Violation of Hund’s third rule in structurally disordered ferromag- nets V. Kapaklis, P.T. Korelis, B. Hjörvarsson, A. Vlachos, I. Galanakis, P. Poulopoulos, K. Özdogan,˘ M. Angelakeris, F. Wilhelm and A. Rogalev Phys. Rev. B 84, 024411 (2011) VI Imprinting layer specific magnetic anisotropies in amorphous multilayers Hossein Raanaei, Hugo Nguyen, Gabriella Andersson, Hans Lidbaum, Panagiotis Korelis, Klaus Leifer and Björgvin Hjörvarsson Journal of Applied Physics 106, 23918 (2009) VII Structural stability and oxidation resistance of amorphous Zr-Al alloys I.L. Soroka, J. Vegelius, P.T. Korelis, A. Fallberg, S.M. Butorin, and B. Hjörvarsson, Journal of Nuclear Materials 401, 38-45 (2010) Reprints were made with permission from the publishers. Other published papers not included in this thesis I Combined light and electron scattering for exploring hydrogen in thin metallic films Jan Prinz, Gunnar K. Pálsson, Panagiotis T. Korelis, and Björgvin Hjörvarsson, Applied Physics Letters 97, 251910 (2010) II Atomic and electronic structure of amorphous Al-Zr alloy films J. Vegelius, I.L. Soroka, P.T. Korelis, B. Hjörvarsson and S.M. Butorin Journal of Physics: Condensed Matter 23, 265503 (2011) Comments on my contribution The objective of this study is to explore the interplay between the structural and magnetic properties of condensed matter. A variety of experimental techniques has been employed and team work has been essential for this purpose, as well as extensive collaborations with other groups and experts in the fields of electron microscopy, neutron and X-ray scattering. I have therefore had the opportunity to participate in a diverse spectrum of activities. A brief description of my individual contribution is given here. Sample making: Prepared all the samples in Papers I, II and IV and the amorphous samples in Paper V. In Paper III, the workload was shared with the first author. Was responsible for the deposition system and assisted the first authors in producing the samples of Papers VI and VII. X-ray characterization: Performed the majority of the X-ray studies in Papers I to V and participated in those of Paper VII. Composition characterization: Performed and analyzed all Rutherford Backscattering measurements that are found throughout this thesis and was taking care of the measurement setup maintenance in the meanwhile. Magnetic characterization: Contributed all the magneto-optic measure- ments and analysis, with the exception of those reported in Paper VI. Participated in the superconducting magnetometry measurements in Paper IV and carried out the rest that are found in this thesis. Also, participated in all the Polarized Neutron Reflectivity and X-ray Magnetic Circular Dicroism beam times that are reported here, and many more. Scientific Writing: The majority of the papers were written in common effort with the co-authors. Shared the workload with the first au- thor in Paper III and had the major responsibility for the writing of Paper IV. Contents Introduction............................................. 11 1 Disorder in Metallic Materials ............................ 15 1.1 Different Aspects of Disorder......................... 15 1.2 The Structure of Amorphous Metals and Alloys............ 17 2 Magnetic Properties .................................... 23 2.1 Basic Concepts.................................... 23 2.2 Amorphous Fe and FeZr Alloys........................ 35 2.3 Amorphous CoZr and FeCoZr Alloys................... 38 3 Experimental Methods in Practice ......................... 41 3.1 Thin Film Deposition................................ 41 3.1.1 Sputtering.................................... 42 3.1.2 Growth Modes................................. 47 3.2 Structural and Composition Characterization.............. 49 3.2.1 X-ray Scattering............................... 50 3.2.2 Transmission Electron Microscopy................. 62 3.2.3 Rutherford Backscattering Spectrometry............. 64 3.3 Magnetic Characterization............................ 72 3.3.1 Magneto-Optic Kerr Effect........................ 73 3.3.2 X-ray Magnetic Circular Dicroism................. 76 3.3.3 SQUID Magnetometry........................... 79 3.3.4 Polarized Neutron Reflectometry................... 81 4 Research Highlights .................................... 85 4.1 Properties of Fe91Zr9/Al2O3 Multilayers................. 85 4.2 Achieving Highly Amorphous Fe100 xZrx Layers........... 90 − 4.3 Properties of Fe100 xZrx/Al100 xZrx Multilayers........... 92 4.4 Comparing Amorphous− FeZr and− CoZr Thin Films......... 96 4.5 The Induced Moment in Zr........................... 98 4.6 Imprinted Magnetic Anisotropy........................ 100 4.7 Thermal Stability of Al100 xZrx Alloys.................. 102 Populärvetenskaplig Sammanfattning− .......................... 105 Acknowledgments ........................................ 109 Bibliography ............................................ 113 Introduction I. From lodestone to the advances in nanotechnology Ever since the discovery of the mineral magnetite (lodestone), magnetic ma- terials and the study of magnetism and related phenomena have occupied a central place in scientific research and technological progress. Early research studies were focused on understanding the fundamental properties of naturally occuring ferromagnetic elements. The magnetism of the transition metals Fe, Co, Ni and the more intricate magnetic structure of rare earths, Gd, Dy and Tb, have since been thoroughly investigated and reported. The main scientific objectives have been to establish the connection between magnetism and structure and to develop an understanding about the origin of ferromagnetism as well as the forces that mediate magnetic interactions. It was later discovered that certain alloys of magnetic materials exhibited enhanced properties compared to their respective consituents. The magnetic properties of the alloys can be tailored by using different element combina- tions and adjusting the composition. This way, intrinsic material properties such as the size of the magnetic moment, the Curie temperature, magnetic anisotropy and magnetostriction can be tuned in a straighforward manner. Magnetic phenomena have been harnessed in the development of many commodities and technological innovations that have become essential in modern life. Magnetic materials have been engineered to meet the demands of a large variety of applications. Soft magnetic materials with small anisotropy and magnetostriction, e.g. permalloys (FeNi alloys) are used in power grids and transformers owing to low energy losses. On the other hand, materials with large anisotropy which impels a specific magnetization direction, e.g. Nd2Fe14B alloys, have been used as permanent magnets and also in information storage devices. The large diversity that characterizes the range of desired applications underlines the necessity to be able to engineer materials with novel magnetic properties. A breakthrough in materials research came about with the transition from bulk systems to systems with reduced dimensions, signifying the dawn of the age of nanotechnology. The object of nanomagnetism is the study of phenom- ena and properties involving materials that have at least one dimension in the 11 9 nanoscopic range, from 1 (1 nm = 10− m) to 100 nm. The most significant development is the additional possibility for tailoring magnetic properties by changing the physical extension of the material [1]. Due to the emergence of new phenomena, the magnetic behavior of sam- ples with nanometric dimensions can present important differences compared to macroscopic systems. These differences have their origin in reduced phys- ical extension that is in the range of the characteristic length scale of many physical processes and interactions. Another reason is the higher proportion of surface (or interface) atoms for nanoscopic objects, which is associated with broken translation symmetry. This resuls in sites with reduced coordination number, broken exchange bonds and possibly, magnetic frustration [1]. Another influencing factor that can lead to modified magnetic properties in nanostructured materials is the immediate environment. For example, in thin films, strong interactions with the substrate through hybridization can influence the magnetization of the interface layers. The crystal structure of the substrate can also lead to stabilization of a phase that is metastable in bulk. Dependence of magnetic properties on the material and thickness