Low-temperature diffusion, solid state reactions and chemical ordering in Mn-Al thin films

• Applicant: Dr. Igor Veremchuk
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511870118

Considering the emergence of “green” spintronics related to the environmental aspects of producing elementary ferromagnets, much work is devoted to magnetic materials, which contain neither rare-earth elements (like Nd), nor elementary ferromagnets (like Co, Ni and Fe), nor noble metals (like Pt or Pd). In this respect, L10-ordered MnAl thin films are considered very promising for a broad range of applications including permanent magnets, components of magnetic tunnel junctions (MTJs, spin-transfer-torque-type magnetic random access memory (STT-MRAM) or microelectromechanical systems (MEMS). Therefore, at present, the performance of MnAl thin films is often poor compared to bulk values and theoretical calculations. We anticipate that the discrepancy between the bulk and thin film performance (and also related theoretical predictions) is in the strongly different stability of the ordered phase and different kinetics responsible for the formation of the ordered phase in thin films. This is even more facilitated by the fact that the phase diagram for thin films is yet to be established and might be strongly different from the one known for bulk MnAl alloys. Typically, the existing methods to produce L10-MnAl thin films as well as bulk include steps, which require the alloy synthesis under thermodynamic conditions. In many cases, it leads to formation of the multiphase samples. In contrast to that, we will perform the synthesis, starting with a room-temperature-deposited Mn/Al bi-layers, which are subsequently proceed by ion-beam radiation in combination with the temperature treatment to realize the formation of structurally ordered L10-MnAl phase in kinetic limit. Still, having the optimized thin films of MnAl alloy prepared relying on diffusion-induced grain boundary migration solid state reaction (DIGM-SSR), we will address one of the relevant technological fields, where MnAl alloys are considered as promising materials. Namely, we will attempt the realization of exchange coupled composites (ECC) relying on DIGM-SSR fabricated MnAl (magnetically hard alloy) coupled to a soft material. The ultimate advantage of our concept is to lower the phase formation temperature in Mn/Al-based stacks by activating DIGM-driven SSR based on low-temperature diffusion processes and facilitated by the ion-beam treatment. For the production of L10-MnAl thin film using DIGM-SSR mechanism a Mn/Al bi-layer will be deposited at room temperature and post-annealed (<600°C). The deposition at room temperature will minimize the diffusion between metal layers and no thermodynamically stable MnAl binary phases will be formed. To date, no same or similar approach has been reported in the literature. From the fundamental point of view, we will provide not only deep understanding of the chemical transformation nature in Mn-Al thin films. We will be able to construct a proper thin-film-relevant phase diagram at low temperatures.

• DFG Programme: Research Grants
• International Connection: Ukraine
• International Co-Applicant: Dr. Igor Vladymyrskyi