Soft in HArd MAgnetic Nanocomposites – SHAMAN

A magnet’s energy product, which quantifies the work that can be done by the magnet, is a key figure of merit for comparing magnets. The energy product of magnets doubled in value every 12 years in the last century, due to the discovery of new hard magnetic phases with improved intrinsic properties and the development of appropriate microstructures through complex processing techniques. The emergence of RE-TM magnets has revolutionised the design of motors and generators, and Nd-Fe-B based magnets are now of crucial importance for strategic value chains, in particular electric power generation (wind power, hydro power), transport (hybrid electric vehicles), and electronics (computers, mobile phones).
The growth in energy product has been practically stagnant over the last 20 years since no new magnetic phases having intrinsic properties better than those of Nd2Fe14B have been discovered, while the room temperature energy product achieved for NdFeB-based magnets is close to it’s theoretical limit. An elegant approach to significantly increase the energy product of permanent magnets, is to produce a nano-structured composite material that combines a hard magnetic phase exchange coupled to a high magnetisation soft phase. The phenomenon was initially discovered by Coehoorn and the concept developed by Kneller and Hawig. Skomski and Coey showed that, the length scale of the soft phase should be on the order of the domain wall width of the hard phase—a few nanometers—and they suggested that it may be possible to achieve an energy product in excess of a megajoule per cubic meter in an optimized hard/soft nanocomposite.
Efforts to produce hard/soft nanocomposites have since been carried out using bulk metallurgical, chemical and thin film synthesis. In the vast majority of studies, the energy product attained was inferior to that of single-phase magnets, while no studies reported significantly enhanced energy products. This is because of the non-concomitant attainment of sufficiently small soft magnetic elements with a narrow size distribution (affects coercivity and loop shape), texture of the hard magnetic phase (affects remanence and loop shape), and full density of the overall structure (affects remanence). Additionally, recent theoretical work by Skomski indicates that soft-in-hard structures should have higher coercivity than hard-in-soft structures.
The objective of the SHAMAN project is to examine the true potential of hard-soft nanocomposite materials for the development of magnets, with properties surpassing those of today’s high-performance magnets. For this purpose, the project will:
- use tools of modern nanoscience (Low Energy Cluster Beam Deposition and e-beam Lithography) to produce thin film models of ultra-strong hard magnets based on exchange coupled soft-in-hard nanocomposites
- exploit unique lab based and Large Scale Facility (X-ray Magnetic Circular Dichroism spectroscopy) based advanced magnetic characterisation tools to demonstrate the crucial link between sample processing and extrinsic magnetic properties
- develop modelling to guide the research and assess the results obtained.

Such magnets would have a significantly reduced RE content compared to today’s high performance RE-TM magnets. This is important in light of the so-called “RE-crisis”, caused by very serious concerns with the sourcing and pricing of RE elements.
The experimental demonstration of the potential of hard-soft nanocomposites should feed into studies on processing of ultra-strong bulk magnets. Beyond this, high energy product hard magnetic thin films have great potential for use in micro/nano-systems.