430
I. de Moraes and N. M. Dempsey
(XMCD) spectroscopy is one such technique [75]. XMCD was used to measure
reversal of the hard phase in hard/soft NdFeB and PrFeB-based ribbons, and comparison with global magnetisation reversal curves measured by classical magnetometry
was used to extract soft phase reversal [76]. A spectacular illustration of full element
selective reversal was reported for hard/soft DyFe 2 /YFe 2 heterostructures [77, 78].
XMCD was also used to study interphase exchange coupling in hard/soft Sm–Co/Fe
bilayers with a gradient in the thickness of the Fe layer [79]. XMCD can be performed
with soft (low energy) or hard (high energy) x-rays, the low probing depth of soft
x-rays limits it to surface studies while XMCD with hard x-rays can be used to
probe bulk properties. Hard X-ray MCD under high magnetic fields and at variable
temperature [80] holds great potential for the advanced magnetic characterisation of
hard-soft magnetic nanocomposites.
17.4 Conclusions
Despite much effort and some progress, the promise of the hard-soft nanocomposite
concept to produce ultra-strong magnets has not been realised to date. Initial efforts
were based on bulk metallurgical synthesis and physical vapour deposition. More
recently, much effort has gone into exploiting the unique advantages offered by chemical synthesis, to prepare hard-soft nanocomposites with controlled size and composition of the constituent phases. So far, the approach has been successfully applied
to the fabrication of hard-soft composites with FePt (Pd) and SmCo-based hard
phases. Further enhancement of the energy product achieved requires compaction to
full density, alignment of the hard phase and increased coercivity, if such magnets
are to match or go beyond today’s high-performance NdFeB magnets. Extension
of the approach to form nanocomposite magnets with mid-range energy products,
based on a range of rare earth free hard magnetic materials, could free up rare earths
presently used in bonded magnets, for use in high energy product magnets. Chemically synthesised hard-soft nanocomposite powders could also be used to make
micro/nanosized magnets, using emerging fabrication techniques such as micromagnetic imprinting [81] and 3D-printing [82], for applications in bio-medicine,
microrobotics and micro/nanosystems.
Acknowledgements The authors acknowledge funding from the French National Research Agency
(project N° ANR-16-CE09-0019-01).
References
1. O. Gutfleisch, M.A. Willard, E. Brück, C.H. Chen, S.G. Sankar, J.P. Liu, Adv. Mater. 23,
821–842 (2011)
2. J.M.D. Coey, Magnetism and Magnetic Materials (2010)
I. de Moraes and N. M. Dempsey
(XMCD) spectroscopy is one such technique [75]. XMCD was used to measure
reversal of the hard phase in hard/soft NdFeB and PrFeB-based ribbons, and comparison with global magnetisation reversal curves measured by classical magnetometry
was used to extract soft phase reversal [76]. A spectacular illustration of full element
selective reversal was reported for hard/soft DyFe 2 /YFe 2 heterostructures [77, 78].
XMCD was also used to study interphase exchange coupling in hard/soft Sm–Co/Fe
bilayers with a gradient in the thickness of the Fe layer [79]. XMCD can be performed
with soft (low energy) or hard (high energy) x-rays, the low probing depth of soft
x-rays limits it to surface studies while XMCD with hard x-rays can be used to
probe bulk properties. Hard X-ray MCD under high magnetic fields and at variable
temperature [80] holds great potential for the advanced magnetic characterisation of
hard-soft magnetic nanocomposites.
17.4 Conclusions
Despite much effort and some progress, the promise of the hard-soft nanocomposite
concept to produce ultra-strong magnets has not been realised to date. Initial efforts
were based on bulk metallurgical synthesis and physical vapour deposition. More
recently, much effort has gone into exploiting the unique advantages offered by chemical synthesis, to prepare hard-soft nanocomposites with controlled size and composition of the constituent phases. So far, the approach has been successfully applied
to the fabrication of hard-soft composites with FePt (Pd) and SmCo-based hard
phases. Further enhancement of the energy product achieved requires compaction to
full density, alignment of the hard phase and increased coercivity, if such magnets
are to match or go beyond today’s high-performance NdFeB magnets. Extension
of the approach to form nanocomposite magnets with mid-range energy products,
based on a range of rare earth free hard magnetic materials, could free up rare earths
presently used in bonded magnets, for use in high energy product magnets. Chemically synthesised hard-soft nanocomposite powders could also be used to make
micro/nanosized magnets, using emerging fabrication techniques such as micromagnetic imprinting [81] and 3D-printing [82], for applications in bio-medicine,
microrobotics and micro/nanosystems.
Acknowledgements The authors acknowledge funding from the French National Research Agency
(project N° ANR-16-CE09-0019-01).
References
1. O. Gutfleisch, M.A. Willard, E. Brück, C.H. Chen, S.G. Sankar, J.P. Liu, Adv. Mater. 23,
821–842 (2011)
2. J.M.D. Coey, Magnetism and Magnetic Materials (2010)