Magnetic properties of hard-soft amorphous nanolaminates

Sammanfattning: Amorphous magnetic thin film heterostructures and multilayers are often used in data storage as well as spintronic devices. Spintronics will help the next generation of nano-electronic devices to increase their memory and processing power and reduce their power consumption. This thesis focuses on the developments of hard and soft amorphous thin films as well as soft/hard multilayers, with an emphasis on the optimization of these materials for use in, for example, spintronics applications. The key for optimization lies in the understanding of the fundamental relationships between structural disorder, composition, and macroscopic magnetic properties.The first part of thesis presents a systematic combinatorial study of composition-structure-property relationships in amorphous alloy thin films of SmCoTi and CoZr, with a particular emphasis on tuning the coercivity µ0Hc ordering temperature Tc, and saturation magnetization Ms with composition. It has been found that 5-7 at.% Ti increases the room temperature coercivity approximately by a factor of ~ 2 (maximum µ0Hc ≈ 0.2 T) compared to amorphous SmCo for Co content in the range 80-85 at.%. For CoZr, dilution of Co with Zr decreases the overall Co moment and the ordering temperature. In magnetic multilayered device architectures, these amorphous alloys might be appropriate for use as soft layers (CoZr) or tunable pinning layers (SmCoTi), depending on the application.This thesis also explores the combination of amorphous hard (SmCo or SmCoTi) and soft (CoAlZr) alloys in bilayer, trilayer, and multilayer structures. The sandwiched of hard and soft amorphous layers that are produced by magnetron sputtering exhibit well-defined interfaces without any lattice strain. First-order reversal curve measurements show that the amorphous hard and soft phases are rigidly exchange-coupled, i.e., the soft phase moment always follows the magnetization direction of the hard phase, for up to at least 20 nm thickness. It is easy to imprint uniaxial in-plane anisotropy in these samples. Both the coercivity and the anisotropy constant increase significantly, by a factor of approximately 4, with increased interface density in the case of CoAlZr/SmCoTi multilayers. In soft/hard/soft trilayers with the same materials, thermal stability is enhanced compared to a single hard layer. Experimental results presented in this thesis demonstrate the potential for tuning properties important to applications based on thin films and multilayers.