Rare Elements in Magnetic Materials · 2011-12-21 · Physics of Magnetic Materials Group (Yamagata...
Transcript of Rare Elements in Magnetic Materials · 2011-12-21 · Physics of Magnetic Materials Group (Yamagata...
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Rare Elements in Magnetic Materials
WPI Advanced Institute Materials Research Tohoku University
Terunobu Miyazaki
JST Japan-EU workshop, Nov. 22, 2011
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My Research Experience• 1972-1975 : hcp Ni, fcc Co, Fe-Co-Ni• 1975-1985 : Rapidly quenched amorphous materials,
Sndust (Fe-Al-Si) alloys• 1985-1991 : Amorphous thin films (Gd-Co, ・・・),Spin-
glass (Fe-based alloy), Magnetiresistance (Fe,Co,Ni)• 1991-1993 : Tunnel magnetoresistance, Soft magnetic
materials, Multilayer films, Kerr effect of alloy films• 1993-2007 :Tunnel magnetoresistance, (Magnetism of
organic materials), (Permanent magnet), HDD, MRAM• 2007- : MRAM materials, Organic/In-organic hybrid
materials
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Price of the Elements used for Magnetic Materials
Elements Price ($/kg)B 0.65N
Mg 2.7 (2005)Al 2.2 (2010)Si 2.49V 16Cr 7.6Mn 0.003Fe 0.06Co 67Ni 37Zn 3.2
Elements Price ($/kg)Ga 530Ge 1240Ru 1400 (2011)Pd 11500Ir 37000 (2011)Pt 42100Nd 45→460Sm 250Gd 140Tb 800→4900Dy 150→3800
At 2007
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レアメタルニュース(発行元:アルム出版社)2010 年 03 月 24 日p01 抜粋
Dy
Nd
Nd
Dy
Tb
June 2010~August 2011
2005~2010
Price of rare earth elements
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: used for magnetic materials
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Classification of magnetic materials
• Spintronics materials : Fe-Co-B, Heusler alloys (Co2MnSi), Pt-Mn, Ir-Mn, Co-Pt, Fe-Pt, CoCrPt , Mn-Ga
• Hard magnetic materials : NdFeB+Dy, SmCo, FeSmN
• Soft magnetic materials : Fe-Ni, Permendur (CoFe), Fe-based amorphous alloys, Sendust (Fe-Al-Si)Except oxides
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Staff of Spintronics Materials Group and Collaboration
Materials physics in AIMR
TOSHIBA
Dept. Appl. Phys RIEC
T. Miyazaki S. Mizukami
T. Kubota Q. Ma
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Our Target
Finding a new material which will be used as the electrodes of MTJ in high density MRAM
Ms < 300 Gauss
K⊥ = 1x107 erg/cc
α < 0.01
TMR ratio > 100 %
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TMRdevice
MOS-FET
Large magnetic friction
(Large write current)
Low magnetic frictionLarge perpendicular magnetic anisotropy
Thermal fluctuation(Memory is lost)
Spintronics Materials for Gbit STT-MRAM
K⊥ > 10 Merg/cc α < 0.01
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- 5 0 - 2 5 0 2 5 5 0- 3 0 0
- 2 0 0
- 1 0 0
0
1 0 0
2 0 0
3 0 0
I n - P l a n e
P e r p e n d i c u l a r
M (
emu/
cc)
H ( k O e )
Wu et al, APL 94, 122503 (2009), Mizukami et al, PRL 106, 117201 (2011), Kubota et al, APEX 4, 043002 (2011)
Large ( K⊥ =1-2x107
erg/cc ) perpendicular anisotropy
Small damping constant
α=0.01-0.02
TMR ratioWe must improve this point
0 20 40 60 80-60
-50
-40
-30
-20
-10
0
Kerr
sign
al (a
rb. u
nit)
Delay time (ps)Delay time (ps)
0.83
0.430.28
0.12 (mJ/cm2)Pump laser fluence
Ker
r si
gnal
(ar
b. u
nit)
Typical magnetic and transport properties for Mn-Ga thin film (green Material) developed in our group
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Perpendicular magnetic anisotropy, K⊥ > 10 Merg/cc
D. Weller et al. IEEE Trans Mag. 36 10 (2000)
FePdCo3Pt
CoPt
Co5SmFePt
Fe14Nd2B
CoCrPt
Noble or Rare-earth metals are crucial ?
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Mn-Ga alloys exhibit large-K⊥ as well as low-α
10-2 10-1 100 101
10-2
10-1
α o
r αef
f.
Kueff (Merg/cm3)
FePt
[Co/X]N(X=Ni,Pd,Pt)
CoCrPt MgO/CoFeB
Mn-Ga
GaMn
Mn
And also low-cost
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40 45 50 55-3
-2
-1
0
1
2
3
Ku(
q) (m
eV/c
ell)
q (1/cell)
b
MnII : 2.48 µB
MnI : -3.09 µBMs = 306 emu/cc
Comparison Comparison between experiments and theorybetween experiments and theory
LMTO-ASA with LDA approximation
minority
majority
-6 -4 -2 0 2
-10
0
10
Den
sity
of s
tate
s(
1/eV
uni
t cel
l)
E-EF (eV)
S. Mizukami et al., Phys. Rev. Lett. 106, 117201 (2011).
K⊥ = 26 Merg/cc
Calc. including spin-orbit interaction
MnIIMnIGa
Electron number per cell
Ku
(meV
/uni
t cel
l)
Roughly consistent with exp. values
Mn 3
Ga
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Small damping is only around EF, (between DOS peaks)
small
large
(still under investigation)
PossiblePossible story ?story ?
∆EξK2SO∝⊥
( )F2
2SO ED
∆Eξα ∝
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Physics of Magnetic Materials Group (Yamagata University)
Prof Kato
・ Development technology for reducing Dyusage in a rare-earth magnet
METI-NEDO Project : Rare Metal Substitute Materials DevelopmentProject (H19-H23)
Yamagata Univ. + 2 Univ. +2 Institute + 4 Companies
・ Coercivity enhancement in bulk Nd-Fe-B by high-magnetic field process
・ Coercivity mechanism study by using model-interface sample made by thin-film process
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Progress of energy product (BH)max
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50
45
40
35
30
10 15 20 25 30
MRI, Speaker
Electric Vehicle(Dy 10%)
HDD, CDDigital Camera
ABS sensor
OA / FA motor
Servo motor
Air ConditioningRobot, Generator
Hc (kOe) required at 20 oC
(BH
) max
(MG
Oe)
Operating Temperature (℃)50 150 250
(Dy 0%)
(Dy 5%)
Natural Abundance : Dy << Nd
Main use and corresponding magnetic properties of Nd-Fe-B permanent magnet
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Nd-Fe-B permanent magnet
Dy-free
Dy 10%
Tc =310˚C
How to increase the coercive force without Dy?
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Single domain
Reverse domain
Uniform domain
Interface control
Disordered surface
Ⅰ.Reduction of particle size Ⅱ.Control of particle surface
Particle size (μm)
Hc(kOe) Multi-domain
0.3
90
Two approaches to increase Hc of Nd-Fe-B magnet without Dy
Hc ( Dy-free Nd-Fe-B ) ≒ 10 kOe
This value is approximately 10 % of the theoretically expected value
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tNFB (nm)
702075
ΔHc= 10 kOe
without Nd overlayer
with Nd overlayer+ post-annealing
多underlayer
Nd2Fe14B single crystal Nd overlayer
Hc enhancement in Nd-Fe-B film by Nd capping
多underlayer
Nd2Fe14B single crystal
Dgrain(nm)
Hc
(kO
e)
t NdFeB(nm)
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21
Hc versus size
size control
Sintered Magnets (Intermetallics)
Interface control
(YU)
0.01 0.1 1 10 100Grain Size D (μm)
Coe
rciv
ityH
c(k
Oe)
11
10
100
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Any effect of mag. force by field gradient ?
Problems of Dy diffusion process
Effect of Strong Field Gradient on Hc in the grain boundary diffusion process
・ Max. diffusion depth : 3-5 mm
・ Strong Dy-content gradient from
surface to inside
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*annealed at Ta=500˚C after diffusion
Cu 0.1% Nd-Fe-B
electric furnaceDy(3μm)
F ∝ H•dH/dz
18 T superconducting magnet
magnetic force:
Dy diffusion experiment in strong field gradient
Tdiffusion = 850˚C, 60 min
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Dy (KDyS
< 0)
Nd (KNd > 0)
c Dy (KDy > 0)
土浦ら、固体物理14, 677 (2009), まてりあ 50, 389 (2011)
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-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
-2.0-1.5-1.0-0.5 0.0 0.5 1.0 1.5 2.0
M /
Ms
H / Hk
Dy layer = 10
31
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0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12 14 16 18 20
Hc /
Hk
Dy
J = 9.6 meV
J = 4.8 meV
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How to get replaced materials ?
• Multilayer film• Fine particle• Hybrid• Nano-porous• Interface control• Topological control• ・・・
• Rapid quenching• Sputtering• MBE• Atomic layer deposition• High magnetic field
processing• ・・・
Morphology Change Technical Methods
We need beyond these changes
We must find further other new methods