Lecture

Transcription

Lecture

Recent development of rare earth lean
permanent magnets
Viorel POP
Babeş-Bolyai University, Faculty of Physics,
400084 Cluj-Napoca, Romania
The Scientific research has been conducted by the group of magnetism at UBB
in collaboration with the following teams:
Olivier Isnard
Institut Néel , CNRS, Université Joseph Fourier, Grenoble, France
Ionel Chicinas
Materials Science and Technology Dept., Technical University of Cluj-Napoca, Romania
Jean Marie Le Breton
Groupe de Physique des Matériaux, Université de Rouen, Saint Etienne Du Rouvray, France
Mihaela Văleanu
National Institute of Material Physics, P.O. Box MG-7, R-76900 Magurele, Bucharest, Romania
With the financial supported of
Romanian Ministry of Education and Research, grant PN-II-ID-PCE-2012-4-0470
Outline
•
•
•
•
•
Introduction
MnBi magnetic phase
MnAl magnetic phase
Nanocomposites magnets=Spring magnets
Conclusions
Outline
•
•
•
•
•
Introduction
MnBi magnetic phase
MnAl magnetic phase
Conclusions
 magnetic materials are critical components in many
devices and for advanced technologies.
 high performance magnet (HPM)/wind generator 10001600 kg/MW.
 motors and generators: 2 kg HPM/hybrid electric vehicle20 million vehicles by 2018.
 Magnetocaloric applications 4 kg HPM/kW cooling power.
 high performance magnet (HPM)/wind generator 10001600 kg/MW.
 motors and generators: 2 kg HPM/hybrid electric vehicle20 million vehicles by 2018.
 Magnetocaloric applications 4 kg HPM/kW cooling power.
HPM= rare-earth based magnets
China manages about 96 % of
rare-earth resources in 2011
!!!
REE price fluctuations
PrNd alloy
1800
0746491981
July,2011
1599RMB/kg
1600
RMB/kg
1200
Price
1400
600
1000
July,2013
357.5RMB/kg
800
400
200
0
2010/7/2
July,2010
240.5RMB/kg
2011/7/2
2012/7/2
2013/7/2
The price of PrNd alloy have increased about 565% form November 2010 to
July 2011. In July 2013, it drop to 22.4% compare with top price.
Instability of RE market, ex. Nd: 150 $/kg/2013; 450 $/kg/2011, 15 $/kg/2009
REE price fluctuations
DyFe alloy
July,2011
14292RMB/kg
16000
Price RMB/kg
14000
12000
10000
8000
6000
July,2013
1495RMB/kg
July,2010
1340RMB/kg
4000
2000
0
2010/7/2
2011/7/2
2012/7/2
2013/7/2
The price of DyFe alloy have increased about 967% form July 2010 to July
2011. In July 2013, it drop to 10.46% compare with top price.
Kaihong Ding - Yantai Shougang Magnetic Materials, China, Energy and Materials Criticality Workshop, Santorini 2013
Solutions
?
?
Yes, we are obliged to have solutions !
Solutions
1. The increase of usage efficiency.
2. Recycling.
?
Solutions
1. The increase of usage efficiency.
2. Recycling.
3. New magnetic phases without rare-earth with high magnetic properties for
applications as permanent magnets and magnetic refrigeration.: Fe-Co si FeNi tetragonal, Fe-Co ternary or quaternary, Fe16N2, MnBi, MnAl, Mn3Ga,
Heusler alloys
4. Soft/hard nanocomposite magnets  Spring magnets
Rare Earth-Free Permanent Magnets ?
RE-free hard magnetic compounds exist: FePt, CoPt, MnBi, MnAl, Zr2Co11, ε-Fe2O3
Even the Alnico-type magnets still have a room for improvement; their theoretical
(BH)max is 36-49 MGOe and they have excellent temperature stability; Artificial Alnicos!
Compound
Structure
Saturation
magnetization
Curie temperature
(oC)
Anisotropy
constant K1
(MJ/m3)
(BH)m
(MGOe)
Co
hexagonal
17.6 kG
1115
0.53
FePt
tetragonal
14.3 kG
477
6.6
CoPt
tetragonal
10.0 kG
567
4.9
Co3Pt
hexagonal
13.8 kG
727
2.0
MnAl
tetragonal
6.2 kG
377
1.7
9.6
MnBi
hexagonal
7.8 kG
357
1.2
16-17
BaFe12O19
hexagonal
4.8 kG
450
0.33
3-4
Zr2Co11
orthorhombic(?)
≈70 emu/g
500
? (HA = 34 kOe)
14
ε-Fe2O3
orthorhombic
≈16 emu/g
?
? (Hc = 23.4 kOe)
Alnico
Cubic (shape)
12-14
SmCo5
hexagonal
11.4 kG
681
17.0
25-30
Nd2Fe14B
tetragonal
16.0 kG
312
5.0
30-57
8-11(36)
G. Hadjipanayis, Delaware University, Energy and Materials Criticality Workshop, Santorini 2013
?
Solutions
1.
2.
3.
The increase of usage efficiency.
Recycling.
New magnetic phases without rare-earth with high magnetic properties for
applications as permanent magnets and magnetic refrigeration.: Fe-Co si FeNi tetragonal, Fe-Co ternary or quaternary, Fe16N2, MnBi, MnAl, Mn3Ga,
Heusler alloys
Our recent research in these directions
1. New magnetic phases without rare-earth with high magnetic properties
 MnBi
 MnAl
• Mn50+δAl50-δ; δ=4
• Mn50Al50-δXδ; δ=4, X=Ni, Zn, Ti
 hard magnetic phases of SmCo5, SmCo3Cu2, R2Fe14B
 soft magnetic phases of -Fe, Fe-Co (~20 or 10 wt%)
 MnBi
 MnAl
• Mn50+δAl50-δ; δ=4
• Mn50Al50-δXδ; δ=4, X=Ni, Zn, Ti
 hard magnetic phases of SmCo5, SmCo3Cu2, R2Fe14B
• SmCo5
large anisotropy
• SmCo3Cu2
large coercivity
• R2Fe14B
best magnets
 soft magnetic phases of -Fe, Fe-Co (~20 or 10 wt%)
Outline
•
•
•
•
•
Introduction
MnBi magnetic phase
AlMn magnetic phase
Conclusions
MnBi magnetic phase
 Low temperature phase (LTP)-NiAs type Hexagonal (Ferromagnetic)
 High temperature phase (HTP) -Distorted Ni2In type hexagonal (paramagnetic)
MnBi magnetic phase
 Low temperature phase (LTP)-NiAs type Hexagonal (Ferromagnetic)
 High temperature phase (HTP) -Distorted Ni2In type hexagonal (paramagnetic)
 Quenched high temperature phase (QHTP)-Orthorhombic (Ferromagnetic-low Ms)
Some previous works in MnBi magnetic compound*
Powders: Sintered method & magnetic separation
(BH)max=7.7 MGOe
Nanocrystalline MnBi by melt-spinning technique
(BH)max = 7.1 MGOe
(powders of meltspun ribbons)
(powders)
J B Yang et al. J. Phys.: Condens. Matter 14 (2002) 6509
Hot pressed bulk magnet
Yang et al. Appl. Phys. Lett. 99, 082505 (2011)
Spark plasma sintered bulk magnet
(BH)max< 2 MGOe
(BH)max=4.3 MGOe
Density: 93%
Density: 90%
Adams et al. J. Appl. Phys. 23 1207 (1952)
Zhang et al. J. Appl. Phys 109, 07A722 (2011)
*G. Hadjipanayis, Delaware University, Energy and Materials Criticality Workshop, Santorini 2013
Magnetic properties of MnBi/Sm2Fe17Nx nanocomposite powders
 MnBi powders: Hc of 12.4 kOe with Mr of 55 emu/g
 Sm2Fe17Nx powders: Hc of 7 kOe with Mr of 130
 Hybrid magnet powders exhibit
•
Hc and Mr values intermediate to those of pure
MnBi and Sm2Fe17Nx
• anisotropic magnetic characteristics with Mr/Ms ratio
greater than 0.91
G. Hadjipanayis, Delaware University, Energy and Materials Criticality Workshop, Santorini 2013
Our main results
MnBi
Synthesis:
 melting : Mn and Bi of 99,99% purity (1 wt % Mn in excess)
 annealing : 258-420ºC/ from 2 hours to 4 days
 mechanical milling: of bulk MnBi phase for 2 hours
X-rays powder diffraction:
 Kα radiation of copper in the angular range 2θ = 20 - 100 and
 Kα1 radiation of cobalt in angular range 2θ= 20 - 80º
Magnetic measurements:
 extraction method in a continuous magnetic field of up to ± 10 T
MnBi: influence of annealing
Bi
MnBi
Bi
MnBi Ta = 420°C/4days
MnBi Ta=420 °C/4days
Intensity (arb units)
MnBiMnBi
TaTa
=400
°C/24 h
= 400°C/24h
= 400°C/2h
MnBiMnBi
TaTa
=400
°C/2 h
MnBiMnBi
TaTa
=300
°C/2 h
= 300°C/2h
MnBi
TaTa=258
°C/24 h
MnBi
= 258°C/24h
MnBi_melt
MnBi_as
melted
20
30
40
50
60
70
80
90
100
2 θ angle (deg)
MnBi: influence of annealing; XRD Cu Kα radiation
Bi
MnBi
Bi
MnBi Ta = 420°C/4days
MnBi Ta=420 °C/4days
Intensity (arb units)
MnBiMnBi
TaTa
=400
°C/24 h
= 400°C/24h
= 400°C/2h
MnBiMnBi
TaTa
=400
°C/2 h
MnBiMnBi
TaTa
=300
°C/2 h
= 300°C/2h
+ 2h MM Ta=400 °C/30 min.
+ 2h MM Ta=350 °C/30 min.
MnBi
TaTa=258
°C/24 h
MnBi
= 258°C/24h
+ 2h MM Ta=300 °C/30 min.
MnBi_as melted
MnBi_melt
MnBi Ta=300 °C/2 h
20
30
40
50
60
70
80
90
100
2 θ angle (deg)
MnBi: influence of annealing; XRD Cu Kα radiation
MnBi: influence of milling; XRD Co Kα radiation
60
MnBi Ta=400°C/2h-4K
60
40
40
20
20
0
2
M (Am /kg)
2
M (Am /kg)
-20
0
-20
MnBi 2hMM Ta=300°C/30min-4K
-40
-40
-60
-5
-4
-3
-2
-1
0
1
2
3
4
5
-60
-3
H (T)
-2
-1
0
H (T)
M(H) for different T,
MnBi melted samples, annealed at 400ºC for 2 h
1
MnBi 2hMM2Ta=300°C/30min-400K
3
Hysteresis loops for different T,
MnBi 2h MM+TT 300 ºC/30 min
Important coercivity at high temperature,
competition with REPM
Outline
•
•
•
•
•
Introduction
MnBi magnetic phase
MnAl magnetic phase
Conclusions
Mn-Al magnetic phase
ε phase –
antiferromagnetic hexagonal structure
τ phase –
L10- ferromagnetic tetragonal structure
ε phase –
antiferromagnetic hexagonal structure
τ phase –
L10- ferromagnetic tetragonal structure
ε' phase –
Intermediate ferromagnetic ordered
orthorhombic phase
Mn54Al46- the best results
•
•
Phase transformation proposed by Broek et. al. with intermediate ordered orthorhombic phase (B19) denoted by ε'.
Acta Metall.,27(1979) 1497
Phase formation, microstructure, magnetic properties of the Mn–Al–C; bulk or MM*
τ-phase nucleates almost exclusively at
the ε-phase grain boundaries
*Q. Zeng, I. Baker, J.B. Cui, Z.C. Yan, JMMM, 308 (2007) 214–226
 DSC: the transformation ε(ε’) τ phase,
 τ –phase stabilized by C doping,
 C doping cannot prevent the formation
of the equilibrium phases from the
metastable ε -phase during annealing.
 DSC: the transformation ε(ε’) τ phase,
 τ –phase stabilized by C doping,
 C doping cannot prevent the formation
of the equilibrium phases from the
metastable ε -phase during annealing.
The optimal magnetic properties for the MM samples, Hc=4.8 kOe, Mr=45 emu/g and Ms= 89 emu/g,
were obtained for Mn54Al46 annealed at 400 °C for 10 min
ε'-phase
τ-phase.
τ- MnAl
1a
Sites
1b
ε'-phase
τ-phase.
Al
Mn
K. Anand et al. / Journal of
Alloys and Compounds 601
(2014) 234–237
(b) the 3d partial
density of states of
Mn at the 1a site
(a)the
total
density of states
(c) the 3d partial
density of states of
Mn at the 1b site of
the P4/mmm unit
cell
stoichiometric MnAl (red curves)
Mn50+δAl50-δ; δ=4 (blue curves) .
τ- MnAl
1a
Sites
1b
ε'-phase
τ-phase.
Al
Mn
Our results
Mn50Al46Ni4 and Mn54Al46
-
Ingots were prepared by arc or induction melting
Different heat treatment to stabilize the desired magnetic phase
Measurements
- Differential thermal analysis (DTA)
- XRD on Brüker D8 Advance diffractometer
- Thermomagnetic measurements up to 800 K
DTA_Mn50Al46Ni4 and Mn54Al46
14
As-cast induction melted
Al Mn
2
12
3
DTA (µV)
10
8
T
e'
T
t
t
t
C
C
e+g
6
4
2
0
100
200
300
400
500
600
700
800
o
T ( C)
Fig. 1. DTA curve for the as-cast Mn50Al46Ni4 alloy.
900
XRD_Mn50Al46Ni4 and Mn54Al46
Mn50Al46Ni4
Thermomagnetic studies
Paramagnetic behavior
300
as-cast
o
TT 470 C 5 h
-1
c (mol/emu)
250
200
150
100
50
650
700
750
T (K)
800
S1 P42
Outline
•
•
•
•
•
Introduction
MnBi magnetic phase
MnAl magnetic phase
Conclusions
a magnetit magnet (1750)
A ferrite magnet (1940)
10 cm
rare earth based magnet (1980)
exchange-spring magnets
(20??)
All this magnets have the same energy !
Nanophased materials behave differently from their macroscopic counterparts
because their characteristic sizes are smaller than the characteristic length
scales of physical phenomena occurring in bulk materials.
Exchange interactions
l sc 
First
neighbours
μ0Hsc ~ 1000 T
Fe :  ~ 30 nm
Nd2Fe14B :  ~ 5 nm
 
2 Asc
0 M s2
Dipolar interaction
(demagnetised field)
lsc~ 3 – 7 nm
A
K
 ~ 4 – 100 nm
Magnetocrystalline anisotropy
Energy dependent of 
Magnetic configuration
in magnetic nanostructures:
domains, walls, vortex, confi
guration magnetic
anisotropy, etc
E. De Lacheisserie (edit.), Magnetisme, Presses Universitaires de Grenoble, 1999.
Theoretical predictions:
Best magnets on the market:
(BH)max  500 kJ/m3
(BH)max = 1090 kJ/m3 for
nanostructured multilayers
Sm2Fe17N3/Fe65Co35
R. Skomski, J. Appl. Phys. 76 (1994) 7059
Kronmuller & Coey Magnetic Materials, in
European White book
on Fundamentel Research
in Materials Science
Max Planck Inst. Metallforschung,
Stuttgart, 2001, 92-96
Experimental realisations: ??????????
high
anisotropy
hard phase
+
exchange
large
magnetization
soft phase
Exchange spring magnets
Structure
Microstructure
Soft-hard exchange hardness
high
anisotropy
hard phase
+
exchange
large
magnetization
soft phase
Dcr  2h
 h   Ah / K h
Dcr = soft phase critical dimension
h = width of domain wall in the hard phase
Ah and Kh are the exchange and anisotropy constants
SmCo5/-Fe Core-Shell Nanocomposite Magnet
Fukunaga
1000
6.4 nm
12.8 nm
25.6 nm
38.4 nm
51.2 nm
64.0 nm
Trilateral Workshop on Critical
Materials, Tokyo, March 2012
(BH)max
800
600
Nd2Fe14B
400
200
0
20
40
60
80
100
Fraction of -Fe [%]
 Fukunaga predicted a drastic increase in (BH)max of SmCo5/-Fe as a function of
-Fe fraction. The Dresden Group (Neu et al) obtained similar results in
SmCo5/Fe multilayers (Intermag 2012). Very recently Hono’s Group
fabricated Fe/Nd-Fe-B multilayers with (BH)m=61 MGOe (Advanced
Materials, 2012).
IEEE TRANS. MAGN., 48 (2012) 3599,
V. Neu , S. Sawatzki , M.Kopte , Ch. Mickel , and L. Schultz
3 layers
5 layers
460 kJ/m3
Volker Neu, Energy and Materials Criticality
Workshop, Santorini 2013
Effect of different surfactants on the formation
and morphology of SmCo5 nanoflakes*
oleylamine (OY),
trioctylamine (TOA)
oleic acid (OA),
* Liyun Zheng, Baozhi Cui, George C. Hadjipanayis, Acta Materialia 59 (2011) 6772–6782
micro-size powders became flakes.
oleylamine (OY),
oleic acid (OA),
oleylamine (OY),
oleic acid (OA),
Our researches
•hard magnetic phases of SmCo5, SmCo3Cu2, R2Fe14B
•soft magnetic phases of -Fe, Fe-Co (~20 or 10 wt%)
SmCo5
SmCo3Cu2
R2Fe14B
large anisotropy
large coercivity
best magnets
Our researches
•hard magnetic phases of SmCo5, SmCo3Cu2, R2Fe14B
•soft magnetic phases of -Fe, Fe-Co (~20 or 10 wt%)
SmCo5
SmCo3Cu2
R2Fe14B
large anisotropy
large coercivity
best magnets
Magnetic Hard/Soft nanocomposites – Spring magnets
(SmCo5, SmCo3Cu2, R2Fe14B)+x% (-Fe or Fe65Co35
• composition, x= 10 or 22 wt % Fe
• milling time
• conventional annealing/short time annealing
Material
•milling of the powders in a high energy planetary mill
preparation •heat treatments (temperatures and duration)
Starting materials :
•
•
•
hard magnetic phases
ingots – prepared by melting
Fritsch Pulverisette 4
Fe NC 100.24 powder (Höganäs), (< 40 μm) and
Fe65Co35 obtained by melting
Mechanical milling experiments:
•
•
premilling of hard and soft magnetic ingots
hard magnetic + -Fe (or Fe65Co35) mixed powders – milled in Ar for 1.5 – 12 h
Annealing:
•
•
conventional annealing:
short time annealing:
in vacuum/450-650 °C for 0.5 up to 10 h.
in argon/700, 750 or 800 °C for 0.5 to 3 min.
Material
characterisation
•X-rays diffraction (XRD)
•DSC measurements
•Electron microscopy (SEM and TEM)
morphology
chemical composition checked by EDX
•Magnetic measurements
cooling
Nd2Fe14B
Fe/Fe3B
release
internal stress
heating
Nd2Fe14B – 6hMM
Classical annealing
S. Gutoiu, V. Pop et al., J. Optoelectron. Adv. Mater. 12 (2010) 2126-2131
Atomic-Scale Investigation
R. Lardé, J-M. Le Breton, A. Maître, D. Ledue, O. Isnard, V. Pop
and I. Chicinaş, J. Phys. Chem., 117 (2013) 7801
Short time annealing
high
anisotropy
hard phase
+
exchange
large
magnetization
soft phase
M
Hard-soft
exchange coupled
H
Hard - soft
uncoupled
120
200
150
100
80
M(Am2/kg)
100
50
0
-50
2
M(Am /kg)
-100
-150
60
-200
-10
-5
0
 H (T)
5
10
0
40
Nd Fe B+10%Fe
2
20
14
8hMM
0
8h MM
o
8h MM+550 C/1.5h
o
-20
8h MM+750 C/1.0min
o
8h MM+750 C/1.5min
o
8h MM+750 C/2.0min
-40
-0.8
-0.6
-0.4
-0.2
0
0.2
 H (T)
0
Nd2Fe14B + 10 % α-Fe; 8h MM
Classical annealing
Short time annealing
Hc- evident increasing
Mr- small decreasing
The influence of the type of hard magnetic phase
500
(Nd
0.92
Dy
400
) Fe B+22 wt% Fe
0.08 2
SmCo +20 wt% Fe_
14
5
milled for 6h
T = 300K
400
350
8hMM
o
8hMM+450 C/0.5h
300
dM/dH (Am /kgT)
6h MM
o
6h MM+450 C/1.5h
300
dM/dH
o
o
6h MM+600 C/1.5h
o
6h MM+650 C/1.5h
200
o
8hMM+550 C/1.5h
250
o
8hMM+600 C/0.5h
2
6h MM+550 C/1.5h
o
8hMM+500 C/1.5h
o
6h MM+800 C/5min
o
8hMM+650 C/0.5h
200
150
100
100
50
0
0
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
µ H (T)
o
1
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
 H (T)
0
R2Fe14B/Fe
SmCo5/Fe
Lower coercivity
Two peaks,
pour hard/soft magnetic coupling
Higher coercivity
One peak,
good hard/soft magnetic coupling
1
150
SmCo Cu +30 wt% Fe
3
T = 300K
100
1.5h MM
3h MM
5h MM
7h MM
9h MM
50
the importance of the
150
0
100
intrinsic anisotropy*
SmCo Cu +30 wt% Fe
3
2
T = 300K
50
M (emu/g)
M (emu/g)
2
-50
0
-50
-100
SmCo3Cu2 2h MM
3h MM
3h MM+450C/0.5h
7h MM
7h MM+450C/0.5h
-100
-150
-8
-4
0
4
8
 H (T)
0
-150
-8
-4
0
4
8
 H (T)

*D. Givord, O. Isnard,, V. Pop, I. Chicinas, JMMM 316 (2007)
This behavior was connected with coercivity mechanism of the
SmCo3Cu2 phase given by the microstructure [1-2] and diminishing
of the intrinsic coercivity by Co substitution with Cu [3].
[1] E. Estevez-Rams, J. Fidler, A. Penton, J.C. Tellez-Blanco, R.S. Turtelli, R. Grossinger, J. Alloys
Compounds, 283 (1999) 327.
[2] P. Kerschl, A. Handstein, K. Khlopkov, O. Gutfleisch, D. Eckert, K. Nenkov, J.-C. Te´ llezBlanco, R. Gro¨ ssinger, K.-H. Mu¨ ller, L. Schultz, J. Magn. Magn. Matter. 290–291 (2005) 420.
[3] E. Lectard, C.H. Allibert, R. Ballou, J. Appl. Phys. 75 (1994) 6277.
SmCo5
SmCu5
The influence of the hard/soft ratio
0.6
SmCo5+x% Fe (x=20 or 30),
milled 6 and 8 h and annealed at 550°C for 1.5 h*
0.5
150
SmCo +x%Fe
0.4
5
100
c
 H (T)
T = 300 K
Nd2Fe14B+10%Fe
0.3
8hMM
0
2
M (Am /kg)
50
0
0.2
-50
0.1
o
700 C
o
750 C
6h/550oC-1.5h_20%Fe
o
800 C
o
6h/550 C-1.5h_30%Fe
-100
o
8h/550 C-1.5h_20%Fe
0
o
8h550 C-1.5h_30%Fe
2hMM_SmCo
0
5
0.5
1
1.5
2
2.5
annealing time (min)
-150
-6
-4
-2
0
2
4
6
µ H (T)
0
350
SmCo +x wt% Fe_6 h MM
5
T = 300 K
300
30 %Fe as milled
2
dM/dH (Am /kgT)
250
o
30 %Fe 550 C/0.5h
o
30 %Fe600 C/0.5h
200
o
30 %Fe 650 C/0.5h
20 %Fe as milled
o
20 %Fe 450 C/0.5h
150
o
20 %Fe 550 C/1.5h
o
20 %Fe 600 C/0.5h
100
50
0
-5
-4
-3
-2
-1
0
1
µ H (T)
o
*V. Pop, O. Isnard, D. Givord, I. Chicinas, JMMM 310 (2007) 2489
V. Pop, O. Isnard, D. Givord, I. Chicinas, J. M. Le Breton, JOAM 8 (2006) 494
V. Pop et al., J. Alloys Compd. (2011)
V. Pop et al. , J. Alloys Compd. 581 (2013) 821–827
S1 P41
Conclusions
 MnBi LTP: large coercivity at high temperature  a good candidate for performance spring magnets
 MnAl: stabilisation of τ with conservation of Mn moments
 The structure and microstructure  strong impact on hard/soft exchange hardness.
 Intrinsic anisotropy
 the strength of the interphase exchange coupling
 Annealing linked to the recrystallisation temperature of soft phases and hard magnetic phases;
recover the crystallinity of the hard phase and hinder the increase of Fe crystallites.
 For higher α-Fe concentration the magnetic properties are pourer because non correlation with Fe
size crystallites.
 The short time annealing is more appropriate for higher coercivity of the nanocomposites.
Thank you for your attention
This contribution was supported by the
Romanian Ministry of Education and Research, grant PN-II-ID-PCE-2012-4-0470

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