Work Supported by DOE ARPA-E

23 Pages·2011·3.34 MB·English

by  Cole Groff

WavePro
 Conference,
 June
 8-­‐11,
 2011
 Crete
 ,
 Greece

Department
 of
 Physics
 &
 Astronomy,
 University
 of
 Delaware,
 U.S.A.

[email protected]
Work Supported by DOE ARPA-E
Hysteresis Loop
Response
 of
 ferromagne-c
 materials
 to
 magne-c
 field
 (H).

  Area under hysteresis loop
represents the energy losses
which are converted to heat.
M

r
Ms

H

c
B = µο (H + M) (SI)
B = H + 4πM (CGS)
Maximum
 Energy
 Product:
 Strength
 of
 a
 Permanent
 Magnet

(BH) ~ H2 V / V
m ag ag m
The higher the (BH) the smaller the V !
m m
Permanent
 magnet
 materials
 must
 have:

● a
 high
 remanence
 to
 produce
 a
 large
 magneFc
 inducFon.

● a
 high
 H
 to
 avoid
 easy
 demagneFzaFon.

c
● a
 high
 T
 to
 resist
 thermal
 demagneFzaFon.

C
TheoreFcal
 limit
 of
 (BH)
 :

m

 (BH)
 =(4πM /2)2

m s
ApplicaFons
 of
 Permanent
 Magnets

● The
 strength
 of
 permanent
 magnets
 (PMs)
 is
 the
 most
 important
 parameter
 that
 affects

the
 power
 density
 and
 energy
 efficiency
 of
 countless
 devices.

Wind turbines with PM generators Hybrid electric
are very efficient at low wind speeds vehicles are
(M ~1-2 Kg). particularly
m
demanding for
power density of
their PM motors
(M > 1-2 tons)
m
PM hydroelectric
turbine generators
eliminate need for
gearboxes
In this generator buoy,
the floater moves coils
Efficient and fail-safe
relative to the PM to
Inductrack maglev
induce voltages
train
Progress
 in
 High
 Performance
 Permanent
 Magnets

● In
 the
 last
 100
 years,
 (BH)
 increased

 by
 a
 factor
 of
 100.

max
● Current
 advanced
 magnets
 are
 based
 on
 the
 discovery
 of

anisotropic
 compounds–
 SmCo ,
 Sm Co ,
 Nd Fe B.

5 2 17 2 14
Advanced
 Permanent
 Magnet
 Materials

● All
 of
 these
 materials
 have
 one
 thing
 in
 common:

 their
 hard
 magneFc
 properFes
 arise

from
 the
 fundamental
 properFes
 of
 their
 major
 consFtuent
 compound.

● The
 (BH)
 limits
 set
 by
 the
 intrinsic
 properFes
 of
 these
 compounds
 are
 nearly
 reached

max
[(BH)
 =
 (4πM /2)2.

max s
Fundamental magnetic properties of hard magnetic compounds
Compound Saturation Anisotropy Curie Theoretical
magnetization field temperature (BH)
max
Nd Fe B

  16.0
 kG

  67
 kOe
  312
 oC
  64.0
 MGOe

2 14
(57
 MGOe)

Sm Fe N

  15.4
 kG

  140
 kOe
  476
 oC
  59.3
 MGOe

2 17 2.3
Sm Co

  12.5
 kG

  65
 kOe
  920
 oC
  39.1
 MGOe

2 17
(33
 MGOe)

SmCo

  11
 kG

  ≤
 440
 kOe
  681
 oC
  30.2
 MGOe

5
(25
 MGOe)

PrCo

  12.3
 kG

  ≥
 145
 kOe
  620
 oC
  37.8
 MGOe

5
Development
 of
 New
 Advanced
 Permanent
 Magnets

● 
 Probability
 exists
 for
 discovery
 of
 new
 anisotropic
 compounds;
 but

search
 is
 extremely
 difficult.

● Non-­‐rare
  earth
  magnets
  remain
  a
  possibility
  but
  a
  focused
  and

concerted
 effort
 is
 needed
 (97%
 of
 rare
 earths
 produced
 in
 China!).

● 
  A
  new
  concept
  of
  high
  performance
  exchange-­‐coupled

nanocomposite
 magnets
 was
 proposed
 in
 the

 late
 80s
 but
 has
 not

yet
 materialized.
Rare
 Earth-­‐Lean
 Exchange-­‐Coupled
 Nanocomposite
 Magnets

● MagneFc
 exchange
 coupling
 allows
 us
 to
 combine
 the
 high
 coercivity
 of
 rare-­‐earth

compounds
 with
 the
 high
 magneFzaFon
 of
 sok
 magneFc
 materials
 and
 develop
 a

METAMATERIAL:
 composite
 magnet
 with
 performance
 greater
 than
 the
 sum
 of
 the

two.

● According
  to
  models
  (Skomski
  et.al.),
  the
  predicted
  (BH)
  of
  the
  hard-­‐sok

max
composites
 exceeds
 100
 MGOe
 (57
 MGOe
 is
 the
 present
 record
 for
 sintered
 Nd-­‐Fe-­‐B).

● Because
  the
  exchange
  interacFon
  has
  a
  very
  short
  range,
  the
  composite
  material

must
 be
 in
 the
 nanoscale
 (size
 of
 sok
 phase
 ≈20
 nm,
 about
 twice
 the
 domain
 wall

width
 of
 hard
 phase).
Nanostructured Nd-Fe-B Magnets
Single
 Phase

 Isotropic

  Single
 Phase
 Isotropic

  Nanocomposites
  Nanocomposites

Decoupled

  Exchange-­‐coupled
  Isotropic
 Coupled
  Anisotropic
 Coupled

M /M
 =
 0.5
  M /M
 >
 0.5
  M /M
 >
 0.5
  M /M
 >
 0.5

r s r s r s r s
(BH)
 =
 12
 MGOe
  (BH)
 =
 20
 MGOe
  (BH)
 >
 20
 MGOe
  (BH)
 ~
 100
 MGOe

max max max max
Hard phase Soft phase Magnetization
Anisotropic Nanocrystalline Magnets by Die-Upsetting
c - axes c - axes
● Anisotropic
  nanocrystalline
  Nd-­‐Fe-­‐B

magnets
 can
 be
 produced
 by
 die-­‐upseong

at
 high
 temperature
 [R.W.
 Lee,
 Appl.
 Phys.

Lep.,
 46,
 790,
 1985]
 of
 alloys
 with
 an
 over-­‐
stochiometric
 rare
 earth
 content.

Hot-­‐pressed
  Hot-­‐deformed

magnet
  magnet

● It
  is
  difficult
  to
  obtain
  textured
  Nd-­‐
Fe-­‐B
  nanocrystalline
  magnets
  with

under-­‐stochiometric
  rare
  earth

content
  because
  of
  the
  absence
  of

low
 melFng
 Nd-­‐rich
 phase.