PROPERTIES AND APPLICATIONS OF HIGH ... - Vacuumschmelze

emanent polarization B r in T
1,5
1,4
1,3
1,2
1,1
1,0
VACODYM 7xx TP
VACODYM 7xx AP
8 10 12 14 16 18 20 22 24 26 28 30
coercivity H cJ(20°C) in kA/cm
VACODYM 6xx AP
VACODYM 6xx TP
Figure 11: Remanent polarization of sintered net-shape Nd-Fe-B parts, produced by transverse field (TP) or axial field (AP) diepressing
in dependence of the coercivity HcJ(20°C). VACODYM 7xx grades achieve high polarizations and maximum energy
densities. The maximum operating temperatures amount to 50 up to 150°. VACODYM 6xx grades have got stronger coercivities
HcJ and can be operated at temperatures between 110 and 230 °C.
5.2 Applications
Modern permanent magnets enable the design of small and fast disk drives for data storage in computers, a
large number of accessories for automobiles in order to improve safety or comfort, tiny and sensitive sensors,
transducers for acoustic applications, beam guidance assemblies for undulators in order to achieve
brilliant light sources with ultrashort wavelengths, optical insulators for contolling data transmission, and a
large variety of generators and motors. Some small motors with a diameter of 1.9 mm and a length of
5.5 mm speed up to >100 000 rpm and achieve a power of 60 mW for moving microdevices. Besides all
kinds of servo- and linear-motors, there are large machines with a diameter of 3.2 m and a length up to
9.5 m. They are rotating slowly at 120 rpm, but achieve a power of 5 MW for the propulsion of ships. There
are projects for machines with a power up to 18 MW.
Lately more flexible MRI systems have come into application. The patients are no longer confined in a
fixed solenoid or a C-shape magnet system. The magnet assembly resides underneath the patient table
when not in use. At the push of a button a permanent magnet system is elevated to scanning position, so
that intraoperative magnetic resonance imaging has become possible [17]. This procedure enables accurate
imaging during surgery.
Besides part body MRI systems have been developed in order to save time of whole body scanners for major
clinical examinations [18]. Even for pets a variety of MRI systems have come into operation.
Modern computer-controlled magnet assemblies are applied for the navigation of catheters or guidewires,
which contain small permanent magnets at the tip, throughout the cardiovascular system of a patient [19].
The tip of the interventional devices can be digitally controlled within 1 mm by the external fields and
hence facilitates the manipulation of catheters by the physician.
6. Summary
By optimizing the alloy-composition and the processing route Nd-Fe-TM-B magnets with high maximum
energy densities between 305 and 415 kJ/m³ can be produced. The remanent polarizations and coercivities
vary between 1.26 to 1.47 T and 19 to 9.5 kA/cm, grades VACODYM 7xx. Due to the excellent remanent
polarizations, these magnets have got smaller coercivities, what confines the maximum operating tempera-