Rare Elements in Magnetic Materials Terunobu Miyazaki WPI Advanced - - PowerPoint PPT Presentation

Rare Elements in Magnetic Materials

WPI Advanced Institute Materials Research Tohoku University

Terunobu Miyazaki

JST Japan-EU workshop,

• Nov. 22, 2011

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
• rganic materials), (Permanent magnet), HDD, MRAM
• 2007-

: MRAM materials, Organic/In-organic hybrid materials

Price of the Elements used for Magnetic Materials

Elements Price ($/kg) B 0.65 N Mg 2.7 (2005) Al 2.2 (2010) Si 2.49 V 16 Cr 7.6 Mn 0.003 Fe 0.06 Co 67 Ni 37 Zn 3.2 Elements Price ($/kg) Ga 530 Ge 1240 Ru 1400 (2011) Pd 11500 Ir 37000 (2011) Pt 42100 Nd 45→460 Sm 250 Gd 140 Tb 800 →4900 Dy 150 →3800 At 2007

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

： used for magnetic materials

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

Staff of Spintronics Materials Group and Collaboration

Materials physics in AIMR TOSHIBA

• Dept. Appl.

Phys RIEC

• T. Miyazaki
• S. Mizukami
• T. Kubota
• Q. Ma

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 %

TMR device MOS-FET Large magnetic friction (Large write current) Low magnetic friction Large perpendicular magnetic anisotropy Thermal fluctuation (Memory is lost）

Spintronics Materials for Gbit STT-MRAM

K⊥ > 10 Merg/cc α < 0.01

• 5 0
• 2 5

2 5 5 0

• 3 0 0
• 2 0 0
• 1 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 ratio We must improve this point

20 40 60 80

• 60
• 50
• 40
• 30
• 20
• 10

Kerr signal (arb. unit) Delay time (ps)

Delay time (ps)

0.83 0.43 0.28 0.12 (mJ/cm2) Pump laser fluence

Kerr signal （arb. unit）

Typical magnetic and transport properties for Mn-Ga thin film (green Material) developed in our group

Perpendicular magnetic anisotropy, K⊥ > 10 Merg/cc

• D. Weller et al. IEEE Trans Mag. 36 10 (2000)

FePd Co3Pt CoPt Co5Sm FePt Fe14Nd2B CoCrPt

Noble or Rare-earth metals are crucial ?

Mn-Ga alloys exhibit large-K⊥ as well as low-α

10-2 10-1 100 101 10-2 10-1

α or αeff.

Ku

eff (Merg/cm3)

FePt [Co/X]N (X=Ni,Pd,Pt) CoCrPt MgO/CoFeB

Mn-Ga

Ga Mn Mn

And also low-cost

40 45 50 55

• 3
• 2
• 1

1 2 3

Ku(q) (meV/cell) q (1/cell) b

MnII : 2.48 µB MnI : -3.09 µB Ms = 306 emu/cc

Comparison Comparison between experiments and theory between experiments and theory

LMTO-ASA with LDA approximation

minority majority

• 6
• 4
• 2

2

• 10

10

Density of states （ 1/eV unit cell) E-EF (eV)

• S. Mizukami et al., Phys. Rev. Lett. 106, 117201 (2011).

K⊥ = 26 Merg/cc

• Calc. including spin-orbit interaction

MnII MnI Ga

Electron number per cell Ku (meV/unit cell) Roughly consistent with exp. values

Mn3Ga

Small damping is only around EF, (between DOS peaks) small large (still under investigation)

Possible Possible story ? story ?

∆E ξ K

2 SO

∝

⊥

( )

F 2 2 SO

E D ∆E ξ α ∝

Physics of Magnetic Materials Group (Yamagata University)

Prof Kato

・ Development technology for reducing Dy usage in a rare-earth magnet

METI-NEDO Project : Rare Metal Substitute Materials Development Project (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

Progress of energy product (BH)max

50 45 40 35 30 10 15 20 25 30 MRI, Speaker Electric Vehicle (Dy 10%) HDD, CD Digital Camera ABS sensor OA / FA motor Servo motor Air Conditioning Robot, Generator

Hc (kOe) required at 20 oC (BH)max (MGOe) 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

Nd-Fe-B permanent magnet

Dy-free Dy 10%

Tc =310˚C

How to increase the coercive force without Dy?

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

tNFB (nm) 70 20 7 5

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 (kOe) t NdFeB(nm)

21

Hc versus size

size control

Sintered Magnets (Intermetallics)

Interface control

(YU)

0.01 0.1 1 10 100

Grain Size D (μm) Coercivity Hc (kOe)

1 1 10 100

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

*annealed at Ta=500˚C after diffusion

Cu 0.1% Nd-Fe-B

electric furnace Dy(3μm)

F ∝ H•dH/dz

18 T superconducting magnet magnetic force:

Dy diffusion experiment in strong field gradient

Tdiffusion = 850˚C, 60 min

Dy (KDy

S < 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)

• 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 3 1

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

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

• ther new methods