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Fig. 3.16 Historical
overview of the maximum
energy density of permanent
magnets. Modi ed gure,
originally published in [ 16 ];
published with kind
permission of ©
[Vacuumschmelze GmbH
2009]. All Rights Reserved
Figures 3.16 and 3.17 show the historical overview of the maximum energy
density of permanent magnets and different magnetic materials and alloys,
respectively. They have been reproduced from documents available from a Euro-
pean producer of soft and hard magnetic materials [ 16 ], i.e. Vacuumschmelze
GmbH. This company is also involved in the production of La-based magnetoca-
loric materials. Despite the fact that the trend for the increase in the energy density
was similar to that of Moore
s law, we can see from the Fig. 3.16 that developments
in new permanent-magnet materials have not led to any substantial breakthrough in
the past 15 years.
'
3.2.1.1 Ceramic Materials
These materials are also called
. They are manufactured from a composite of
iron oxide combined with BaCO 3 or SrCO 3 . The manufacturing process normally
involves pressing and sintering. These magnets are brittle and have a low energy
product. On the other hand, they are inexpensive, and with the relatively high
coercivity, resistant to corrosion and can be used at higher temperatures. They can be
manufactured as isotropic (the same magnetic properties in all directions) or aniso-
tropic magnets (have a preferred direction of magnetization as a result of particle
alignment during the processing). These magnets are the most widely applied mag-
nets on the market. Their energy product is in the range from 10 to 40 kJ m 3 .
ferrites
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