Replacing critical rare
earth materials in high
energy density magnets
R. William McCallum
Ames Laboratory
Iowa State University
Ames Laboratory is operated for the U.S. Department of Energy by Iowa
State University under Contract No. DE-AC02-07CH11358
•
Permanent Magnet Research at
Ames Lab
Ames Laboratory prime contractor:
–
EERE Vehicle Technologies: Permanent Magnet Development for Automotive Traction Motors
•
Subcontractors:
 University of Nebraska University of Maryland  Brown University
 Oak Ridge National Laboratory  Arnold Magnetic Technologies
–
ARPA-E: Novel high-energy permanent magnet without critical elements
•
Subcontractors:
 General Motors  Molycorp  NovaTorque
•
Ames Laboratory subcontractor:
–
ARPA-E: High Energy Permanent Magnets for Hybrid Vehicles and Alternative Energy
•

University of Delaware,  University of Nebraska  Northeastern University  Virginia Commonwealth University
 Electron Energy  Corporation  Ames Laboratory (Search for new RE-TM-X compounds
ARPA-E: Manganese-Based Permanent Magnet with 40 MGOe at 200°C
 Pacific Northwest National Laboratory
•
EERE Vehicle Technologies: Alternative High-Performance Motors with Non-Rare Earth Materials
Scalable, Low-Cost, High Performance IPM Motor for Hybrid Vehicles


General Electric
EERE Vehicle Technologies:

UQM Inc.
Demand for High Energy Product
Permanent Magnets
Transportation
2015
8,000 tonnes
Wind 2020
16,830
Tonnes
2012
14,200 tonnes
Estimates from
Steve Constantinides
600 kg neo / MW
Why rare earth magnets
5
Requirements for a
Permanent Magnet
• A permanent magnet is an object made from
a material that is magnetized and creates its
own persistent magnetic field.
– Curie temperature > 300 C
– Large magnetic moment per unit volume
– Large anisotropy
• The moment must be fixed in space
Rare-Earth PM Characteristics
Remanence
VACODYM 655 TP
Coercitivity
Energy Density
Temperature coefficient
(RT - 100°C)
Temperature coefficient
(RT - 150°C)
Brtyp.
Brmin.
HcBtyp.
HcBmin.
HcJmin.
(BH)max typ.
(BH)max min.
TK ( Br )
TK ( HcJ )
TK ( Br )
TK ( HcJ )
Hmag
T
T
kA/m
kA/m
kA/m
kJ/m3
kJ/m3
%/°C
%/°C
%/°C
%/°C
kA/m
1.26
1.22
970
925
1670
305
280
• Rare earth NdFeB permanent magnet
• Remanent Flux Density (Br): 1.1 T
• Resistivity of 1.4e-6 -m
7
-0.090
-0.61
-0.100
-0.55
2500
Non-Rare-Earth PM Characteristics
Product
Alnico 5-7
Remanence
Coercitivity
Energy Density
Temperature
coefficient
(RT - 100°C)
Temperature coefficient
(RT - 150°C)
Brty
p.
Brmi
n.
HcBty
p.
HcBmi
n.
HcJmi
n.
(BH)max
typ.
(BH)max
min.
TK ( Br )
TK ( HcJ )
TK (
Br )
TK (
HcJ )
Hmag
T
T
kA/m
kA/m
kA/m
kJ/m3
kJ/m3
%/°C
%/°C
%/°C
%/°C
kA/m
1.3
1.2
57.6
56.0
26.7
-0.02
• Non-rare earth permanent magnet
• Remanent flux density (Br) 1.3 T
• Resistivity of 7.5e-7 -m
8
0.01
Rare Earth vs. Non-Rare Earth PM Materials
Characteristics
Rare Earth PM1
Non-Rare Earth PM
Remanent Flux Density
(Br)
1.0-1.47 T
1.3 T
Coercitivity
(Hc)
770-1065 kA/m
57.6 kA/m
Energy Density
(BH)
200-380 kJ/m3
26.7 kJ/m3
Max Operating Temperature
120-240ºC
530ºC
What magnet properties are needed by a machine designer ?
• High remnant flux density—probably high enough now
• High operating temperature—high enough now
• Much higher coercive force
• Higher resistivity
9
Fe-Co
Fe
Fe-Ni
Magnetocrystalline Anisotropy
c
c
c
b
a
b
a
c
Energy
c
a
b
c
c
b
a
b
a
a
b
a
c
c
b
Angle
b
a
a
b
Building in lattice anisotropy
RE is the bigger atom, due to 4f’s
12
1.8
Rule of Mixtures
BHmax limited by Ms
60
1.4
50
1.2
1
40
0.8
30
0.6
Nd-Fe
20
0.4
10
0.2
40
wt% Fe
13
60
80
1-12
20
1-17
0
2-14
1-5
0
0
100
BHmax (MGOe)
Saturation Magnetization, M s (T)
1.6
70
Nd2Fe14B
Beyond Rare Earth Magnets (BREM):
Magnetic Materials by Design
• Bringing modern tools and understanding of
magnetism together
– A multi-disciplinary approach
– Need consistent set of metrics and goals
• Informed by PM targets from motor designers
• Each of the disciplines needs to provide close
feedback and guidance to the others.
• We need to work hand-in-hand with motor
designers.
Theory and Modeling
BREM
Genetic
Algorithm
(i)
(j)
(k)
(l)
Anisotropy
Calculations
Characterization
of Co-W Cluster
Combinatorial
Synthesis
Characterization
of Alnico
Characterization
Liquid
phase
Synthesis
Synthesis
State of the Art: Permanent Magnets
Nanostructured: (a) layered
and (b) granular (proposed
by Skomski and Coey 1993)
•Atomically structured
(Nd2Fe14B, since 1984)
Challenges to Discovery
• While basic the tools exist
– Need to overcome some intrinsic issues
• Density functional theory (DFT) is currently limited to cell sizes of a
few hundred atoms
• Incorporating magnetism in DFT is computationally intensive
• Exchange interactions occur over 10’s of nm
– atomistic to meso-scale
– Combinatorial studies limited to thin films
• Scale-up to bulk materials
– Chemical synthesis
• Control of grain boundary chemistry and thickness
TEAMS:
BREM Thrust Structure
Theory and Modeling Group
Members:
(ORNL) Malcolm Stocks
(Ames) Kai-Ming Ho, Vladimir Antropov, CZ Wang, Bruce Harmon, Matt Kramer
(Univ. NE-Lincoln) Ralph Skomski, Dave Sellmyer
(Univ. MD-College Park) Ichiro Takeuchi
Characterization Group
Members:
(Ames) Matt Kramer, Bill McCallum, Bruce Harmon
(Univ. NE-Lincoln) Jeff Shield, Dave Sellmyer
(Univ. MD-College Park) Ichiro Takeuchi
(Brown Univ.) Shouheng Sun
Synthesis Group
Members:
(Ames) Bill McCallum, Matt Kramer, Iver Anderson
(Univ. NE-Lincoln) Jeff Shield, Dave Sellmyer
(Univ. MD-College Park) Ichiro Takeuchi
(Brown Univ.) Shouheng Sun
18
Routes to Better Non-Rare Earth
Permanent Magnets
• Improve on known systems
– Enhanced knowledge of coercivity mechanisms
– Enhanced control of composition and
microstructure
• Discover new primary phases (helped by theory)
– High Curie temperature
– High Magnetization
– Magnetic anisotropy
Theoretical Efforts at Ames Laboratory
Two Thrusts:
1. Theoretical phase diagram exploration and structural optimization
2. Magnetic properties calculations
Structures
Chemical Composition
quantum
mechanics
calculations
Structure
Prediction
Magnetic
Properties
Phase diagrams
& Structures
•Ab initio energies (include magnetic interactions) &
efficient configuration search algorithm (e.g, GA)
•Empirical potentials (e.g., tight-binding) & efficient
configuration search algorithm; further refine by ab
initio calculations
Computational Materials Design from First-Principles
Given chemical compositions
•The number of possible structures are huge
•Need efficient configuration search algorithm
(e.g., genetic algorithm)
•Need powerful computers
Example
Identify structure candidates
Compute the energies & properties Magnetic structures and properties can also
of the candidate structures
be predicted accurately by ab initio quantum
mechanics calculations
Select the candidates with
desirable properties
Length & Time Scales in
Magnetism
10-6
Time Scale (s)
Micromagnetics
10-9
Spin Models
10-12
Quantum
10-10
10-1510-4
22
10-8
10-6
Length Scale (m)
Theoretical Efforts in BREM Thrust
• Conduct searches for binary systems to provide candidate
structures and compositions for magnetic property
calculations and experimental studies.
– Fe-based alloys
– Inclusion of magnetic interactions in energy evaluation
• Extend searches to ternary systems and provide candidate
structures and compositions for magnetic property
calculations and experimental studies.
• Our goal is to develop reliable computational tools that can
identify the materials and compositions that have stable
structures and desired magnetic properties for experimental
synthesis.
Composition Spreads of
Ternary Metallic Alloy Systems
Mn
3” spread wafer
Mn
Co-sputtering scheme
Ni
Al
Ni
Al
Phase diagram
Composition is mapped using an electron probe (WDS)
Meso-scale Modeling
• Given intrinsic properties of constituent
phases
– What is optimum phase distribution?
– What is optimum microstructural scale?
– What role do interactions between grains play?
– What are the maximum properties we can expect
to achieve?
Semihard Phases
Semihard phase
improves coercivity of
hard-soft composites
even if <K1> is kept
constant.
Novel High-Energy Permanent Magnets without Critical Elements
R. William McCallum, Ames Laboratory, Ames, IA
Impact
Increase the supply of rare-earth (RE) permanent magnet for electric traction motors by a
factor of 3 to 5 from developed mineral resources.
Low-coercivity, non-RE magnetics are unsuitable for applications to wind or vehicles, Nd 2Fe14B is favored. Ce
abundance is 4x Nd and Pr combined, but suitable Ce-based magnets are undeveloped.
Via integrated computational engineering and advanced synthesis and processing, we will:
• Control and manipulate magnetic properties of Ce-TM permanent magnets for traction motors.
• Develop a Ce-TM based magnet for motors having Tc > 300 C, a remnant magnetization >1 Tesla, and a
coercivity >10 KOe, needed for technology.
0472-1526
Novel high-energy permanent
magnet without critical elements
Project Objective
• Develop a Ce-TM based permanent magnet
with a Curie temperature in excess of 300oC, a
remnant magnetization in excess of 10 kG,
and coercivity in excess of 10 kOe.
28
Novel high-energy permanent
magnet without critical elements
• Not a “rare-earth free” magnet but a “free”
(relatively $ wise) rare-earth magnet
• Not the best rare-earth magnet but much
better than any non-rare-earth magnet
29
Not the “best” RE Magnet but better than any non-RE Magnet!
Above this line
achieves GOAL
30
Why Cerium (Ce)?
• Cerium is not in short supply!
– abundance of Ce 4x Nd and Pr combined
• ~50% of the RE content of Molycorp’s Bastnasite
• Excess of Ce on the market
– Ce–TM–based permanent magnet
• 2 to 3 increase of high-energy RE magnets supply
• No increase in mining or RE metal production
31
Why Ce? Materials Physics
• Cerium, as a rare-earth (i.e., “larger”) atom supports anisotropic structural
motifs of RCo5 and R2Fe14B. Even weakly magnetic Ce!
• Magnetism of Ce atom is easily influenced by adding, e.g. H or N, due to
strong sensitivity of charge/magnetic state on distance between Ce and TM
atom.
• DFT methods properly describe the crucial covalent magnetic effects that
are determined by hybridization, in contrast to Heisenberg-type models for
magnetism in RE permanent magnets that do not describe band effects.
• It is cheaper that all other rare earths!
• And, a team of world leaders in RE magnet materials development,
characterization, and DFT-based alloy characterization/prediction.
• We can design it!
33
Historically, why not Ce?
• In known RE-Transition Metal (TM) magnetic systems
(versus those containing Nd and/or Pr)
– 25% drop in Curie temperature (Tc)
– significant reduction in saturation magnetization (Ms)
– Ce is more 4+ than 3+ (mixed-valency)
• Little 4f contribution to magnetocrystalline anisotropy
• Low coercivity (Hc)
34
Not the “best” RE Magnet but better than any non-RE Magnet!
Above this line
achieves GOAL
35
Why does Ce tend to 4+ valence?
• Why? The atomic electronic configuration
• Ce [Xe] 4f1 5d1 6s2
– So Ce+3 [Xe] 4f1 with 3 conduction electrons
– or Ce+4 [Xe] with 4 conduction electrons
• Nature likes filled shells
36
Magnetic moment per
formula unit in RE-TM
series
37
How do we make Ce+3 ?
• Add conduction electrons
• Expand the lattice
– Ionic Radius
• Ce+3
• Ce+4
• Pr +3
1.034 Å
0.92 Å
1.013 Å
38
State of literature search
• Ce ferromagnets
– 600+ papers
•
•
•
•
•
•
125 on oxides
Ce2TM14B
Ce2TM17
CeTM12
CeTM2
RE-Mn-X
3+ Nd and Ce via Rule of Mixtures
1.8
Rule of Mixtures
BHmax limited by Ms
60
1.4
50
1.2
1
40
0.8
30
0.6
Nd-Fe
0.4
Ce+3-Fe
20
10
0.2
40
wt% Fe
60
80
1-12
20
1-17
0
2-14
1-5
0
0
100
BHmax (MGOe)
Saturation Magnetization, M s (T)
1.6
70
Nd2Fe14B
FM 4+ and 3+ via Rule of
Mixtures
1.8
Rule of Mixtures
BHmax limited by Ms
60
1.4
50
1.2
1
40
0.8
30
0.6
20
Ce+3-Fe
0.4
Ce+4-Fe
10
0.2
40
wt% Fe
60
80
1-12
20
1-17
0
2-14
1-5
0
0
100
BHmax (MGOe)
Saturation Magnetization, M s (T)
1.6
70
Nd2Fe14B
AFM vs FM via Rule of Mixtures
2
Rule of Mixtures
BHmax limited by Ms
60
1.6
1.4
50
1.2
40
1
30
0.8
0.6
20
Ce+3-Fe
0.4
Ce+3-Fe
antiferro
0.2
40
wt% Fe
60
80
1-12
20
1-17
0
2-14
1-5
0
10
0
100
BHmax (MGOe)
Saturation Magnetization, M s (T)
1.8
70
Nd2Fe14B
R2Fe14B and RnFem Tc variation
Structure of R2Fe14B
Reported Substitutions in Nd2Fe14B
T
d ln Tc/dx d ln Ba/dx d ln MFe/dx
(%)
(%)
(%)
Al
-6
-4
-27
Si
+3
-16
-17
Sc
+3
-24
-17
Ti
-20
-37
-26
V
-19
-50
-28
Cr
-8
-8
-17
Mn
-14
-6
-16
Co
+12
-1
+1
Ni
+4
-1
-4
Cu
+1
-10
Ru
-19
-39
-27
C
-8
+27
-7
H
+5
-15
+3
Effect of substitution into Nd2Fe14B.
Elements (except C and H) nominally
substituted on Fe sites. C substitutes for
B and H occupies an interstitial site.
Error! Bookmark not defined.
Magnetic Transitions in Ir-doped CeFe2
Spin-polarized Compton scattering
Magnetic phase diagram of Ce2Fe17
Y. Janssen,* S. Chang, A. Kreyssig, A. Kracher, Y. Mozharivskyj, S. Misra, and P. C. Canfield
PHYSICAL REVIEW B 76, 054420 2007
Competing Phases
Journal of Alloys and Compounds
Volume 509, Issue 24, 16 June 2011, Pages 6763–6767
Anisotropy changes
Novel high-energy permanent
magnet without critical
elements
 Task 1: GM - Interstitially modified cerium-transition metal
(Ce-TM) magnet materials
 Task 2: AMES - Substitutionally-modified Ce-TM magnet
materials.
 Task 3: AMES - (Ce1-xNdx)2Fe14B exchange-coupled
nanostructures
 Task 4: AMES - Theoretical assessment of interstitially and
substitutionally modified Ce-TM magnet material
53