Functional Magnetic Materials and Hydrides
ADVANCED MATERIALS FOR EFFCIENT USE OF ENERGY
Human development has caused a depletion of natural energy resources and climate changes with non-predictable consequences. New energy concepts are required for the future of our industrial society resulting in e.g. an ever increasing emphasis on improving the efficiency of electricity transmission and utilisation and in the progressive replacement of oil-based fuels in transportation by electric motors.
Permanent magnets play an essential role in all these developments and form vital constituents of electric motors and actuators. Phenomena related to the fundamentals, processing and applications of high performance permanent magnet materials are being explored. This includes the determination of intrinsic magnetic properties, investigation of high pulsed magnetic field induced phase transitions, detailed microstructural and micromagnetic analysis as well as the development of novel processing routes. Other aspects such as lifetime, corrosion resistance and recycling of magnetic materials are also being studied. Further, the ability to fabricate magnetic thick films (5-300µm) with tailored magnetic properties is the key to design and development of new and powerful magnetic Micro Electro-Mechanical Systems (MEMS).
Smart magnetic materials are a group of materials with interesting and useful physical and technical properties, which are influenced by the application of an applied magnetic field. This group includes: magnetorheological fluids and composites, giant magnetocaloric materials and magnetic shape memory alloys. These materials can be applied in e.g. aviation, cars, vibration control and seismic protection as well as in medicine, and cooling technology.
A relatively new application of magnetic materials is magnetic refrigeration as an alternative cooling technology. The basis of which is the magnetocaloric effect (MCE), defined as the cooling or heating of a magnetic material when subjected to a varying magnetic field. This technology offers the prospect of an energy-efficient, silent, compact and environment-friendly alternative to the commonly used vapour-compression refrigeration. The main challenges in the realisation of a practical refrigerator are the availability of large amounts of giant magnetocaloric materials exhibiting large magnetic entropy changes in moderate magnetic fields and low hysteretic losses as well as the magnetic field design with a permanent magnet array.
Magnetic shape memory alloys are a new class of magnetically driven active materials that show large strains of up to 10% in Ni2MnGa. The magnetic field induced movement of twin boundaries can be exploited for actuators, sensors and, as it is an energy dissipating process, also for vibration damping devices. One option to overcome the difficult preparation and inherent brittleness of Ni2MnGa is the production of composites consisting of aligned MSM particles suspended in a stiffness-matched polymer matrix. Quaternary systems are studied to defeat the limited thermal stability of Ni2MnGa.
The only known energy carrier with a high energy density and no emission of greenhouse gas is hydrogen. Research and development of solid-state storage of hydrogen - for e.g. zero-emission vehicle propulsion and other mobile applications – is pursued by exploring functional complex hydrides. Typical phenomena related to nanoscale structures such as the increased relevance of surface effects, transport of matter, defects and the existence of new or metastable phases are exploited when developing new materials with high reversible hydrogen storage capacity, good cyclic stability, suitable thermodynamics and kinetics.
The development of new magnetic and hydrogen storage materials with improved properties requires advanced processing and high resolution characterisation techniques.