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Italian School of Magnetism
Franca Albertini
Istituto dei materiali per l’elettronica e il magnetismo (IMEM) del CNR, Parma
Franca Albertini, IMEM-CNR
Magnetic materials for energy
Magnetic materials for energy
Italian School of MagnetismFranca Albertini, IMEM-CNR
Production/Harvesting
Transmission/distribution
Conversion
Electric generatorElectric motor
Transformer
Mechanical to elctrical EElectrical to mechanical E Energy transfer
From N. Dempsey, ESM 2013
Magnetic field driven functional properties:magnetocaloric effect, magnetic shape memory, magnetic hyperthermia, magnetoresistance, magnetostriction…
Properties Exploitation
Functional magnetic materials
Franca Albertini, IMEM-CNR
Fingerprint
Soft magnetic materials:Trasformers, inductors, sensors
M
H
M
H
Hard magnetic materials:Field production: permanent magnets, magMEMS
Memories
Remote manipulation/sensing
Italian School of Magnetism
µµ00HHcc (T)(T)
10-3
10-5
5
Energy paradigms: renewable energy
Italian School of MagnetismFranca Albertini, IMEM-CNR
WORLD ENERGY
OUTLOOK 2016
Energy paradigms: emissions reduction
Franca Albertini, IMEM-CNR
Renewable energy sources
Energy efficient technologies WORLD ENERGY
OUTLOOK 2016
Italian School of Magnetism
Energy paradigms: closing loops
Redefining refuse as a resource
Franca Albertini, IMEM-CNR
NATURE 531 24 MARCH 2016
Italian School of Magnetism
Permanent magnets: application sectors
Franca Albertini, IMEM-CNR
Motors and generators of electric and hybrid cars
Renewed scientific and technological interest
TWO NOTICEABLE EXAMPLES
Direct drive wind turbines
Italian School of Magnetism
H
µ0MR µ0MS
B=µ0(H+M)
µ0HC
BHC
slope: -1(1-N)/N
BHmax
High Remanence, MR
High Coercive field, HC
High Maximum Energy Product, BHmax
Extrinsic properties(microstructure, texture, shape, domain structure)
High Saturation Magnetization, MS
High Magnetic Anisotropy,
Easy-axis system
High Curie Temperature
Intrinsic properties
Permanent magnets: requirements and properties
Franca Albertini, IMEM-CNR Italian School of Magnetism
Hc>MS
Breakthrough in the
‘50s: over the shape
barrier
BHmax (squared
loop) = 1/4 µ0MS2
Easy magnetization directions
Spin reorientation transitions
Uniaxial systemEMCA = K1 sin
2 θ + K2 sin4 θ + K3 sin
6 θ
EMCA = K1 sin2 θ + K2 sin4 θ + K3 sin6 θ + K3 'sin6 θ cos6φ
...)()( 2
3
2
2
2
12
2
1
2
3
2
3
2
2
2
2
2
110+++++= ααααααααα KKKE
MCA
Cubic Symmetry
Hexagonal symmetry
Uniaxial symmetry: bidimensional problem
)cossincossin(cossin 22
1
2242
21θθφφθθ KKKE
MCA++=
Franca Albertini, IMEM-CNR
Magnetic anisotropy - easy magnetization direction
Italian School of Magnetism
A simple case: uniaxial anisotropic system, non interacting singA simple case: uniaxial anisotropic system, non interacting single domains particles le domains particles
EMCA = K1 sin2 θ + K2 sin
4 θ + K3 sin6 θ EZ = −HMS cosγ
ETOT = EMCA + EZ
c-axisM
H
basal plane
θ1=γ+θ
Franca Albertini, IMEM-CNR
Coercivity is maximum in the easy direction
Anisotropy field: maximum limit of coercive field
Magnetic anisotropy – magnetization process
Italian School of Magnetism
HC in real materials: well below the intrinsic limit
Coercivity (Hc) in bulk magnets is a fraction (20-30% ) of the intrinsic upper limit (anisotropy
field, HA)
Microstructure plays a major role:
Texture
Polycrystalline character
Defects and secondary phases at grain boundaries
Local Reduction of exchange and anisotropy
Nucleation and pinning control the starting
and propagation of magnetization reversal
Appropriate microstructure: new optimized processing techniques
Franca Albertini, IMEM-CNR Italian School of Magnetism
Phenomenological treatment
RE-TM intermetallic compounds
Rare earth
effective magnetic moment
Large Magnetocrystalline anisotropy
µeff = gµB J(J +1)
where J=L-S light RE
J=L+S heavy RE
Transition metal
High Curie Temperature
High Ms
Two-sublattice system
Excange coupling between RE and TM
CaCu5 parent structure
Franca Albertini, IMEM-CNR Italian School of Magnetism
Nd2Fe14B
Italian School of MagnetismFranca Albertini, IMEM-CNR
Compound Tc (K) µµµµ0MS(T) K1 (MJ/m3) Crit. single domain
size(nm)
Domain wall
width (nm)
Nd2Fe14B 585 1.6 5 1 214 4
Sm2Co17 1100 1.3 3.3 490 8.6
BaFe12O19 740 0.48 0.32 89 18
Easy-
magnetization
direction
tetragonal
Discovered in 1982
NdFeB – Dy substitution
Italian School of MagnetismFranca Albertini, IMEM-CNR
2 Kg of NdFe B in a hybrid veichle
600 Kg/MW in eolic generatorsHigh torque to weight ratio motors and generators:
fastly increasing demand of high temeperature application:
Partial replacement of Nd by DyO. Gutfleisch et al. Adv. Mat. 23 (2011) 821
Multiscale approaches
Advanced multiscale characterization techniques
Calculations: from the atomic to the micro and
macro scale
Combinatorial approaches
Thin films and nanoparticles as model systems
Materials for permanent magnets: challenges and strategies
Franca Albertini, IMEM-CNR
Intermediate performances
Dy, Tb elimination or reduction Microstructure control,
grain boundary engineering
Exchange coupled nanocomposites
New RE- free materials
Revisitation of materials (oxides, Mn-based),
Increase of the ratio TM/RE
RE- elimination
Y-La intermetallics
Microstructure control, grain boundary engineering
Reduction of Dy content
Diffusion of Dy in the outer shell of NdFeB
Grain size reduction and magnetic grain decoupling with nonmagnetic grain boundary phases
K. Hono et al. Scripta Mater 67 (2012), 530
Towards the elimination of heavy RE
H. Nakamura et al IEEE-TM 41 (2005) 3844
Nanometric Nanometric
dispersiondispersion of two
magnetic phases dsdh
BHBHmaxmax increase exploitable in PM applicationsincrease exploitable in PM applications
E.F. Kneller and R. Hawig,
IEEE T-M 27, 3588 (1991)
Echange-coupled nanocomposites
M=MS, Hc>MS/2, ideal squared hyteresis loop Artificially structured nanocomposite
Multilayer: lhard=2.4 nm, lsoft=9 nm BHmax = 1 MJ/m3
magnetisationhard + softsoft
anisotropy
Skomski’s prediciton: a 1MJoule magnet
Hard phase fraction= 9%; BHmax=1MJ/m3=137 KGOe
Sm2Fe17N3/Fe65Co35
R. Skomski, J. Appl. Phys.76 (1994) 7059
Exchange-spring
magnet regime
Italian School of MagnetismFranca Albertini, IMEM-CNR
Exchange-coupled nanocomposites
Control of the material structure at the nanoscale
Alignment of the esay anisotropy axes of hard phase
Ideal exchange coupling between grains
Nanocomposites
from
nanocrystalline
fine powders
prepared by
chemical methods
Fe50Co50
Fe65Co35
Fe80Co20
Several attempts were performed, but we are still very far from the predictions
A recent result on
SmCo7 phase
N. Poudyal et al Mater. Res. Express 1 (2014) 016103
Critical points:
Italian School of MagnetismFranca Albertini, IMEM-CNR
New materials: obtaining structural distorsion
MnBi, NiAs type hexagonal, thin films and bulk
Difficult to obtain as single phase
Fe-Ni, Tetragonal L10
slow kinetics formation
Template growth of
core/shell nanoparticles,
epitaxial thin films
Maogang Gong and Shenqiang Ren
Chem. Mater., 2015, 27 (22), pp 7795.
L10 FeNi—the mineral
“tetrataenite”—has been characterized using
specimens found in nickel-iron meteorites.
(NWA 6259 recovered from Northwest Africa
is 95 vol. % tetrataenite with a composition of 43 at. % Ni)
Interstitial αααα���� Fe16-N2 thin films and nanoparticles
Meatastable metal-metalloid Heuslers: a promising huge class of materials
SPD measurement
Sample from L. Lewis
Italian School of MagnetismFranca Albertini, IMEM-CNR
N. Demspey in “The magnetism roadmap 2014, J. Phys D Appl. Phys 47 (20014) 333001
The pull of stronger magnets
Italian School of MagnetismFranca Albertini, IMEM-CNR
Italian School of MagnetismFranca Albertini, IMEM-CNR
The refrigeration scenario15% of total worldwide energy consumption involves the use of refrigeration and air
conditioning (IIR 2013): from <5% (temperate zones) up to 80% (tropical islands)
The large cities of developing countries are at tropical latitudes
Bangkok, Tailandia, 60 %
Delhi, India – 55%
Mumbai, India – 50%
Air conditioning demand is inceasing: By 2025, ~1 billion of new citiziens will become
“consumers”: their first purchase will be an air conditioner (McKinsey Global Initiative)
•New refrigeration technology based on the magnetocaloric effect
•Environment-friendly technology
High efficiency 30% higher than vapor compression
Elimination of harmful gases
Low noise
More compact, scalable
Magnetic refrigeration
Franca Albertini, IMEM-CNR
Adiabatic temperature change ∆Tad
( ) ∫
∂
∂
−=∆∆
2
1
),(
),(,
H
HHH
ad dHT
HTM
HTC
THTT
Magneto-thermodynamic effect of magnetic materials induced by the
application/removal of a magnetic field
Neglect pressure change (dp=0),
mechanical stress (dσ=0)
and electric field (dE=0)
Temperature (K)
En
tro
py (
J*K
g/K
)
0
H=0
Hmax
DST
max
0
( )
H H
T H HH
S M MS T dH
H T T
=
=
∂ ∂ ∂ = → ∆ =
∂ ∂ ∂ ∫
max
0
( )
i
x x
i
xxi xT
XS XS T dx
x T T
=
=
∂∂ ∂ = → ∆ =
∂ ∂ ∂ ∫
Maxwell relations
( , , , , ) + dG T H p E SdT MdH Vdp d PdEσ ε σ= − + + +
•Xi is the generalized
displacement (M, V, e, P)
•xi is the generalized force (H, p,
s, E)
i iSdT X dx= − +∑
magnetization discontinuity
MCE is maximum across magnetic transitions (Tc)
Isothermal magnetic entropy change ∆Sm
Equilibrium thermodynamics of reversible processes
Magnetocaloric effect
1881 E. Warburg discovers the magnetocaloric effect
(MCE) in pure Fe
1926-1927 P. Debye e W.F. Giauque suggest to use MCE to
refrigerate
1933 W.F. Giaque e D.P. MacDougall reach 0.25K
through adiabatic demagnetizaton of paramagnetic
salts.
1949
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/194
9/giauque-lecture.pdf
1976 G.V. Brown: pioneeristic work on magnetocaloric effect at
room temperature (Gd) (1978 Los Alamos Steyert)
History
Franca Albertini, IMEM-CNR
1995-1998 K.A. Gschneidner Jr. @ Ames Lab and C.B. Zimm @ Astronautic
Corporation announce the results of their three-year project
Proof-of-priciple unit: it ran for over 5000 hours in 18 months
applied fied = 5T superconducting magnet
Wcool=600 W
Temperature span =10 K
Material: Gd spheres (5 Kg)
1997 K.A. Gschneidner’s group materials with “GIANT MAGNETOCALORIC” effect
V. K. Pecharsky et al. Journal of Alloys and
Compounds 344 (2002) 362–368
Magnetic field induces a structural phase
transition (from para M to Ferro O)
Morellon et al, Phys Rev B 58, (1998) R14 721
Magnetostructural transition
Recent history
General electrics &
Oak Ridge National Labs
First demnstrator,60W, 4-times more expensive than
conventonal refrigerator
20% energy saving
Claim: commercial product in 2020Haier, Astronautics & BASFLow cooling power Refrigerator(20K ∆T max)
Now
Lab scale prototypes
MC coolers: rotational working principleMC coolers: rotational working principle
Pros: Continuous operation, no dead volumes, no energy waste from alternate breaking-
acceleration of moving masses (typical defect of the linear reciprocating design)
Cons: difficult handling of the fluid heat transporter (fluid valves on rotating components)
Franca Albertini, IMEM-CNR
The ideal Magnetocaloric material should have:
High ∆S and ∆tad obtainable by permanent magnets(less than 2T)
Broad operating T range
Low hysteresis, highly eversible effect
Sustain many cycles (mechanical stability)
Be an excellent heat exchanger (fast dynamics)
Be stable on the long run (corrosion-free)
Rely on readily available, non-toxic, non-strategic chemical elements
Low cost large scale production
Magnetic refrigeration is a concerted scientific and technological problem
The effort for novel refrigerators relies on better materials
Materials: requirements and challenges
Franca Albertini, IMEM-CNR
MnAs, MnPGe: high ∆Smag, As replaced by
P and Ge. Low raw material cost,
difficult preparation route
Gd5(SiGe)4 high ∆Smag, ∆Tad high
raw material cost, difficult preparation route
La(FeSi): to increase Tc LaFeSiH
Low cost of raw materials, long term
stability issues for the hydrogenated phase
Ni-Mn-X Heusler alloys: high ∆smag,
∆Tad high
Wide possibility of tailoring order and
kind of transition, and type of
magnetocaloric effect: DIRECT-
INVERSEHysteresis losses and mechanical
stability issues
∆Tad values in a 2T field.From Liu et al. Nature Materials vol.11, p620 (2012)
MnFePSi: high reversible ∆Tad, low raw
material cost.
Towards commercialization
MnFe0.95P0.595B0.075Si0.33
Guillou et al. Adv. Materials 2014
MnFe0.95P0.595B0.075Si0.33
Liu et al. Nature Mater. 11 (2012) 623
Materials overview
Martensitic transformation
between the cubic L21 and a
lower symmetry structure
(5M IC monoclinic)
Magnetically ordered states
Ni.MnGa- the prototypical material
ΔM
Δχ
Conventional shape memory
Interplay between magneic and structural degrees of freedom
Ferromagnetic shape memory Heusler compounds
Martensitic transformation occurs between two phases showing remarkable differences in
the main properties
-structural properties
-magnetic properties
-electronic properties
�Small hysteresis (field, temperature, pressure, stress)
Entropy change
�Suitable martensitic-magnetic critical temperatures
�Volume change at the transformation dTM/dP
�Lattice distorsion dTM/dσ
Temperature
Magnetic field
Pressure
Stress
The transformation can be induced
�Magnetization change at the transformation dTM/dH Critical T can be
changed by applying
an external field
Ni2MnX (X=Ga, In, Sn, Sb) full Heuslers: Key properties
TTMM
280 320 360 400
Su
scep
tib
ility
(a.
u.)
Temperature (K)
220
275
330
385
2.05 2.1 2.15 2.2 2.25
Tra
nsit
ion
tem
pe
ratu
res (
K)
Composition
TC
TAM
TMA
a
TCm
1 2 3 4
2.1 2.2
Ni content (2+x), z=0
Cri
tical T
(K
)
Co-occurrence of magnetic and
structural transitions: first order
transition from low-symmetry
ferromagnet to high–symmetry
paramagnet300 320 340
Su
scep
tibili
ty (
a.
u.)
Temperature (K)
Tuning of critical T
Increase of the magnetization
change at the transformation
Tailoring martensitic and magnetic properties
Ni2+xMn1+yGa1+z
340 360 380
10
20
- ∆S
m(J
/kg K
)
T (K)
30
0300 320 340
0
2
4
6
8H=0- 1.6 T
T (K)
- ∆S
m(J
/kg K
)
4-time increase of the magnetic
entropy change
Franca Albertini, IMEM-CNR
Ni2MnGa shows a negative M
(saturation moment of austenite is lower
than the saturation moment of martensite)
Therefore,
Ni2Mn1.2Ga0.8
0MdT
dH>
0MT
∂ <∂
max
0
( ) 0
H H
HH
MS T dH
T
=
=
∂ ∆ = <
∂ ∫
Since field stabilizes the phase with higher
moment, TM shifts to higher temperatures
Direct MCE
Cooling by adiabatic demagnetization max0
0H
adT→
∆ >
Franca Albertini, IMEM-CNR
S. Fabbrici et al. J. of Entropy 16 (2014) 2204 and referenceces therein
By Co doping Mn-rich comounds: it is possible to tune magnetic & structural transtions:
number, order, nature (from ferro to para or from para to ferro on heating), and critical
temperatures
paramagnetic gap merging of structural and
austenitic TC
Ni50-wCowMn30+jGa20-jw=0, j=0
w=5w=9, j=2
w=5, j=0
j=2
separated
transitions
merging of
structural and
magnetic
transition (TcA)
TC-Martensite
Co-doped Ni-Mn-Ga Heuslers: a playground for magnetism and
structure
Franca Albertini, IMEM-CNR
Ni2Mn(In,Sb,Sn) (and (Ni,Co)2MnGa) show
positive ∆M
(saturation magnetization of austenite is
higher than the saturation magnetization of
martensite)
Therefore,
0MdT
dH<
0MT
∂ >∂
max
0
( ) 0
H H
HH
MS T dH
T
=
=
∂ ∆ = >
∂ ∫
Since field stabilizes the phase with higher
moment, TM shifts to lower temperatures
Inverse MCE
Adiabatic magnetizationmax0
0H
adT→
∆ <
Franca Albertini, IMEM-CNR
Up to now the best Magnetocaloric performers among Heuslers
�Very weak Magnetic moment in
martensite
Coupled with:
�Very strong magnetic moment in
austenite
High ∆M and dTc/dH
Issue!!! Thermal hysteresis
Irreversible cooling!!
Ni 4
5,2
Co
5.1
Mn
36
.7In
13
Ni 4
9.8
Mn
35In
15
.2
Liu et al, Nature Mat. 11 (2012) p 620
Franca Albertini, IMEM-CNR
�Find the right composition:
structural compatibility
Z.
Zh
an
g e
t a
l. A
cta
Ma
ter.
57
(2
00
9)
43
32
�Exploit the multiple response to external
fields
0MdT
dH<
0MdTdp
>
Transformation matrix eigenvalue
λ2=1 means interface matching between
austenite and martensite
the transformation proceeds
through an invariant plane
Franca Albertini, IMEM-CNR
( , , , , ) + dG T H p E SdT MdH Vdp d PdEσ ε σ= − + + +
Barocaloric Electrocaloric
Magnetocaloric Elastocaloric
i iSdT X dx= − +∑
Planes et al, J Phys.: Condens. Matter 21 (2009) 233201
Magnetocaloric effect is one in a family of caloric effects
Thermal, elastic and magnetic variables
Franca Albertini, IMEM-CNR
Calorimetric measurements under hydrostatic pressure
Ni42.2Co8.4Mn32.4Ga15In2.1.
Direct barocaloric effect: |∆S| value larger than the
corresponding magnetocaloric values measured in 1T
Huge discontinuity of lattice parameters and
volume at the transformation
(∆V up to 1.2%, dP/dT up to -60 K/Gpa)Pressure/stress induced martensitic
transformation
Ll. Mañosa et al. Nature Mater. 9 (2010) 478
Milan-Solsona et al. APL 105 (2014) 241901
Barocaloric/elastocaloric effect
Barocaloric/elastocaloric effect
Franca Albertini, IMEM-CNR
Exploitation of magnetization variations
induced by T at the martensitic transformation
Ni45Co5Mn40Sn10
Diffusionless, fast and sharp
transition, small hysteresis,
high magnetization variation
-Magnetization variation due to stress induced martensitic transformation
-Flux variation due to moving parts: combined exploitation shape memory and magnetism
(Kohl, ICFSMA 2013, Boise)
Other harvesting mechanisms
Energy harvesting
Ferromagnetic shape memory materials for energy
Solid state refrigeration:
exploitation of giant caloric effects
(magneto-, baro- or elasto- caloric)
induced by the application of
magnetic field, pressure or stress
ON
OFF
FIELD
Smart applications Actuators, Sensors (temperature , fields pressure)
Energy harvesting
Crossing response of materials to different fields can be exploited