Abstract
In this study, we have investigated amorphous 20-nm-thick Tb/Fe80Co20 multilayer samples with different individual layer thicknesses and their corresponding alloy counterpart. In particular, the structural and magnetic properties were analyzed upon post-annealing. Up to a certain critical thickness of the individual layers in the multilayer, no significant difference between the multilayers and the alloy is observed in their as-deposited states, which indicates the importance of interfacial intermixing. With a further increase in thicknesses of the individual layers, regions with significant larger Tb content emerge, resulting in a reduced effective Tb moment. The loss in perpendicular magnetic anisotropy upon annealing seems to be delayed for multilayers with thin individual layers compared to the alloy sample. We contribute this behavior to the underlying anisotropic short-range order enforced by the multilayer structure, which hinders the structural relaxation process. At higher temperatures, the multilayers strongly intermix and Fe and Co diffuse through the capping layer. This process leads to a strong enhancement of the saturation magnetization at a certain annealing temperature, due to the formation of separated FeCo and Tb-rich TbFeCo alloy layers, until the sample gets oxidized.
Highlights
Ferrimagnetic (FI) heavy rare earth (RE)-3d transition metal (TM) alloys provide high tunability of magnetic properties, such as saturation magnetization and perpendicular magnetic anisotropy (PMA),1–7 and can exhibit zero magnetic moment at the compensation temperature two sub-lattices compensate each other (Tcomp) depending on the alloy composition
We have investigated the magnetic and structural properties of Tb/FeCo multilayers and the corresponding alloy depending on annealing temperatures
Magnetic characterization revealed a decrease in perpendicular magnetic anisotropy and coercivity with increasing annealing temperature
Summary
Ferrimagnetic (FI) heavy rare earth (RE)-3d transition metal (TM) alloys provide high tunability of magnetic properties, such as saturation magnetization and perpendicular magnetic anisotropy (PMA), and can exhibit zero magnetic moment at the compensation temperature Tcomp depending on the alloy composition. PMA is mainly associated with a chemical short-range order, where RETM atom pairs prefer an out-of-plane direction These properties make them a compelling material candidate for a variety of applications. The use of ferrimagnetic RE-TM systems as pinning layers for soft ferromagnetic (FM) films is of high interest.10–18 In this regard, the switching behavior of the soft layer has been intensely studied and led to the term exchange-spring magnets, which has further implications for spintronic devices, such as spin valves and magnetic tunnel junctions.. Many studies have been devoted to ferrimagnetic multilayers (MLs) because of their additional tunability of magnetic anisotropy depending on their individual layer thicknesses.. We have investigated the influence of the multilayer structure of Tb/FeCo on the structural and magnetic properties depending on the annealing temperature and compare the results to their alloy counterparts. Having a detailed understanding of the underlying processes upon annealing is crucial for future spintronic devices operating at elevated temperatures
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