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Critical Materials for Magnetism Critical Materials for Magnetism J. M. D. Coey Physics Department and CRANN, Trinity College Dublin 2, Ireland 1 . Materials used for applications of magnetism Permanent magnets Soft magnets Magnetic

slide-1
SLIDE 1

Tokyo, 21xi 2011

  • J. M. D. Coey

Physics Department and CRANN, Trinity College Dublin 2, Ireland

www.tcd.ie/Physics/Magnetism

Critical Materials for Magnetism Critical Materials for Magnetism

  • 1. Materials used for applications of

magnetism Permanent magnets Soft magnets Magnetic recording

  • 2. Permanent magnets — filling the gap
  • 3. Perpendicular magnetic media and

memory

slide-2
SLIDE 2

1 Introduction 2 Magnetostatics 3 Magnetism of the electron 4 The many-electron atom 5 Ferromagnetism 6 Antiferromagnetism and other magnetic order 7 Micromagnetism 8 Nanoscale magnetism 9 Magnetic resonance 10 Experimental methods 11 Magnetic materials 12 Soft magnets 13 Hard magnets 14 Spin electronics and magnetic recording 15 Other topics Appendices, conversion tables. 612 pages. Available now. 20% discount for INTERMAG. Order direct for £40 + p&p

www.cambridge.org/9780521816144

slide-3
SLIDE 3

Tokyo, 21xi 2011

Critical raw materials Critical raw materials – – EU report EU report

* Platinum group metals Germanium Tantalum

slide-4
SLIDE 4

1. 1. 1.

  • 1. Materials used for applications

Materials used for applications Materials used for applications Materials used for applications

  • f magnetism
  • f magnetism
  • f magnetism
  • f magnetism
slide-5
SLIDE 5

Tokyo, 21xi 2011

4 Be

9.01 2 + 2s0

12Mg

24.21 2 + 3s0

2 He

4.00

10Ne

20.18

24Cr

52.00 3 + 3d3 312

19K

38.21 1 + 4s0

11Na

22.99 1 + 3s0

3 Li

6.94 1 + 2s0

37Rb

85.47 1 + 5s0

55Cs

13.29 1 + 6s0

38Sr

87.62 2 + 5s0

56Ba

137.3 2 + 6s0

59Pr

140.9 3 + 4f2

1 H

1.00

5 B

10.81

9 F

19.00

17Cl

35.45

35Br

79.90

21Sc

44.96 3 + 3d0

22Ti

47.88 4 + 3d0

23V

50.94 3 + 3d2

26Fe

55.85 3 + 3d5 1043

27Co

58.93 2 + 3d7 1390

28Ni

58.69 2 + 3d8 629

29Cu

63.55 2 + 3d9

30Zn

65.39 2 + 3d10

31Ga

69.72 3 + 3d10

14Si

28.09

32Ge

72.61

33As

74.92

34Se

78.96

6 C

12.01

7 N

14.01

15P

30.97

16S

32.07

18Ar

39.95

39Y

88.91 2 + 4d0

40Zr

91.22 4 + 4d0

41Nb

92.91 5 + 4d0

42Mo

95.94 5 + 4d1

43Tc

97.9

44Ru

101.1 3 + 4d5

45Rh

102.4 3 + 4d6

46Pd

106.4 2 + 4d8

47Ag

107.9 1 + 4d10

48Cd

112.4 2 + 4d10

49In

114.8 3 + 4d10

50Sn

118.7 4 + 4d10

51Sb

121.8

52Te

127.6

53I

126.9

57La

138.9 3 + 4f0

72Hf

178.5 4 + 5d0

73Ta

180.9 5 + 5d0

74W

183.8 6 + 5d0

75Re

186.2 4 + 5d3

76Os

190.2 3 + 5d5

77Ir

192.2 4 + 5d5

78Pt

195.1 2 + 5d8

79Au

197.0 1 + 5d10

61Pm

145

70Yb

173.0 3 + 4f13

71Lu

175.0 3 + 4f14

90Th

232.0 4 + 5f0

91Pa

231.0 5 + 5f0

92U

238.0 4 + 5f2

87Fr

223

88Ra

226.0 2 + 7s0

89Ac

227.0 3 + 5f0

62Sm

150.4 3 + 4f5 105

66Dy

162.5 3 + 4f9 179 85

67Ho

164.9 3 + 4f10 132 20

68Er

167.3 3 + 4f11 85 20

58Ce

140.1 4 + 4f0 13

Ferromagnet TC > 290K Antiferromagnet with TN > 290K 8 O

16.00 35

65Tb

158.9 3 + 4f8 229 221

64Gd

157.3 3 + 4f7 292

63Eu

152.0 2 + 4f7 90

60Nd

144.2 3 + 4f3 19

66Dy

162.5 3 + 4f9 179 85

Atomic symbol Atomic Number Typical ionic change Atomic weight Antiferromagnetic TN(K) Ferromagnetic TC(K) Antiferromagnet/Ferromagnet with TN/TC < 290 K Metal Radioactive

Magnetic Periodic Table

80Hg

200.6 2 + 5d10

93Np

238.0 5 + 5f2

94Pu

244

95Am

243

96Cm

247

97Bk

247

98Cf

251

99Es

252

100Fm

257

101Md

258

102No

259

103Lr

260

36Kr

83.80

54Xe

83.80

81Tl

204.4 3 + 5d10

82Pb

207.2 4 + 5d10

83Bi

209.0

84Po

209

85At

210

86Rn

222

Nonmetal Diamagnet Paramagnet BOLD Magnetic atom 25Mn

55.85 2 + 3d5 96

20Ca

40.08 2 + 4s0

13Al

26.98 3 + 2p6

69Tm

168.9 3 + 4f12 56

slide-6
SLIDE 6

Tokyo, 21xi 2011

O Si Si Al Al Fe Fe Mg Mg Ca Ca K Na Na H Others Others

Si4+ O2- Al3+ Fe

Crustal abundances (top 9) All magnetic elements (log scale}

Cr Mn Fe Co Ni Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

  • 1

1 2 3 4 5

Cr Mn Fe Co Ni Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb

3d elements 4f elements

Pm

Log (abundance, ppm) Js (T) TC(°C) Fe 2.15 771 Co 1.81 1087 Ni 0.61 355

Iron is 40 x as abundant as all the other magnetic elements taken together.

Crustal abundances of magnetic elements

slide-7
SLIDE 7

Tokyo, 21xi 2011

Hysteresis Hysteresis

Any macroscopic magnet exhibiting remanence is in a thermodynamically- metastable state.

M (Am-1) H (Am-

1)

Ms Mr H

d

working point coercivityHc

slide-8
SLIDE 8

Tokyo, 21xi 2011

The demagnetizing field The demagnetizing field

M B H

N S

∇B = 0 B = μ0(H + M) Stray field Demagnetizing field Hd ≈ -N M demagnetizing factor 0 ≤N ≤ 1

slide-9
SLIDE 9

Tokyo, 21xi 2011

Magnetic materials for applications

Ni-Fe/Fe-Co (heads) Fe-Si Fe-Si (oriented) Ni-Fe/Fe-Co Amorphous Others Others Alnico Sm-Co Nd-Fe-B Hard ferrite Co- γ Fe 2 O 3 (tapes, floppy discs) CrO2 (tapes) Iron (tapes) Co-Cr (hard discs) Soft ferrite Others Iron

Soft Magnets Hard Magnets Magnetic Recording Hard Magnets Fe, Sr, Ba, Nd, Sm, Co, Dy, Zr Soft Magnets Fe, SI, Co, Ni, Zn, Mn Magnetic Recording Fe, Ni, Co, Ta, Pt

Breakdown of magnetic materials in 2000 - 30 B$

slide-10
SLIDE 10

Tokyo, 21xi 2011

Summary of magnetic properties of useful materials

Tc (°C) Ms (MAm-1) K (kJm-3) λ (10-6) SmCo5 847 0.86 17200

  • Nd2Fe14B

CoPt FePt 315 567 477 1.28 0.81 1.14 4900 4800 1800

  • SrFe12O19

467 0.38 330

  • Fe94Si6

770 1.68 48

  • 7

Co35Fe65 940 1.95 20

  • 60

Ni80Fe20 570 0.83

  • 1

2 (MnZn)Fe2O4 300 0.50

  • 3
  • 5

(NiZn)Fe2O4 590 0.33

  • 7
  • 25

Y3Fe5O12

287 0.14

  • 2
  • 1
slide-11
SLIDE 11

Tokyo, 21xi 2011

The permanent magnet market (~$10B) The permanent magnet market (~$10B)

Sintered Nd-Fe-B Bonded Ferrite

Tonnage production: Ferrite; 1,000,000 Nd-Fe-B; 80,000

Spindle motor

Voice-coil actuator

Sintered Ferrite Bonded Nd-Fe-B Alnico; Fe,Co,Ni,Al Sm-Co; Sm, Co, Fe, Zr,Cu

SrFe12O1

9

Nd2Fe14 B

Nd,Dy,Tb,Fe,Co,B

slide-12
SLIDE 12

Tokyo, 21xi 2011

The Limits The Limits

Curie temperature TC. Should be > 550 K for RT applications Magnetization Ms. Should be as large as possible. Many applications depend on Ms

2

Energy product |BH|max Should be as large as possible for a permanent magnet |BH|max< ¼μ0Ms

2

Coercivity Hc . Should be 0 for soft magnets, > ½Ms for hard magnets.

  • Cost. As low as possible
slide-13
SLIDE 13

Tokyo, 21xi 2011

The Limits The Limits

Curie temperature TC. Should be > 550 K for RT applications Magnetization Ms. Should be as large as possible. Many applications depend on Ms

2

Energy product |BH|max Should be as large as possible for a permanent magnet |BH|max< ¼μ0Ms

2

Coercivity Hc . Should be 0 for soft magnets, > ½Ms for hard magnets.

  • Cost. As low as possible

Magnetic ordering temperature of > 2000 materials αFe2O3 Fe Co Magnetic ordering temperature (K) Highest Néel temperature Highest Curie temperature

slide-14
SLIDE 14

Tokyo, 21xi 2011

The Limits The Limits

Curie temperature TC. Should be > 550 K for RT applications Magnetization Ms. Should be as large as possible. Many applications depend on Ms

2

Energy product |BH|max Should be as large as possible for a permanent magnet |BH|max< ¼μ0Ms

2

Coercivity Hc . Should be 0 for soft magnets, Hc > ½Ms for hard magnets.

  • Cost. As low as possible

Slater-Pauling Curve

Slope -1

m μB

Fe65Co35 Ms =1.95 MAm-1

Cr Mn Fe Co Ni Cu 6 7 8 9 10 11 Valence electrons

slide-15
SLIDE 15

Tokyo, 21xi 2011

The Limits The Limits

Curie temperature TC. Should be > 550 K for RT applications Magnetization Ms. Should be as large as possible. Many applications depend on Ms

2

Energy product |BH|max Should be as large as possible for a permanent magnet |BH|max< ¼μ0Ms

2

Coercivity Hc . Should be 0 for soft magnets, > ½Ms for hard magnets.

  • Cost. As low as possible

Energy product doubled ≈ every 12 years during the 20th century

slide-16
SLIDE 16

Tokyo, 21xi 2011

The Limits The Limits

Curie temperature TC. Should be > 550 K for RT applications Magnetization Ms. Should be as large as possible. Many applications depend on Ms

2

Energy product |BH|max Should be as large as possible for a permanent magnet |BH|max< ¼μ0Ms

2

Coercivity Hc . Should be 0 for soft magnets, > ½Ms for hard magnets.

  • Cost. As low as possible

The main achievement of technical magnetism in the 20th century was mastery

  • f coercivity

1900: 103 < Hc < 105 A m-1 2000: 1 < Hc < 2 107 A m-1

slide-17
SLIDE 17

Tokyo, 21xi 2011

4 Be

9.01

12Mg

24.21

2 He

4.00

10Ne

20.18

24Cr

52.00

19K

38.21

11Na

22.99

3 Li

6.94

37Rb

85.47

55Cs

132.9

38Sr

87.62

56Ba

137.3

59Pr

140.9

1 H

1.00

5 B

10.81

9 F

19.00

17Cl

35.45

35Br

79.90

21Sc

44.96

22Ti

47.88

23V

50.94

26Fe

55.85

27Co

58.93

28Ni

58.69

29Cu

63.55

30Zn

65.39

31Ga

69.72

14Si

28.09

32Ge

72.61

33As

74.92

34Se

78.96

6 C

12.01

7 N

14.01

15P

30.97

16S

32.07

18Ar

39.95

39Y

88.91

40Zr

91.22

41Nb

92.91

42Mo

95.94

43Tc

97.9

44Ru

101.1

45Rh

102.4

46Pd

106.4

47Ag

107.9

48Cd

112.4

49In

114.8

50Sn

118.7

51Sb

121.8

52Te

127.6

53I

126.9

72Hf

178.5

73Ta

180.9

74W

183.8

75Re

186.2

76Os

190.2

77Ir

192.2

79Au

197.0

61Pm

145

70Yb

173.0

90Th

232.0

91Pa

231.0

87Fr

223

88Ra

226.0

89Ac

227.0

62Sm

150.4 105

66Dy

162.5 179 85

67Ho

164.9 132 20

68Er

167.3 85 20

58Ce

140.1

13 8 O

16.00 35

65Tb

158.9 229 221

64Gd

157.3

63Eu

152.0 90

66Dy

162.5 179 85

Atomic symbol Atomic Number Atomic weight Antiferromagnetic TN(K) Ferromagnetic TC(K)

Cost Periodic Table

80Hg

200.6

36Kr

83.80

54Xe

83.80

81Tl

204.4

82Pb

207.2

83Bi

209.0

84Po

209

85At

210

86Rn

222

Metal Radioactive Nonmetal BOLD Magnetic atom 25Mn

55.85 96

20Ca

40.08

13Al

26.98

69Tm

168.9 56

312 96

36

78Pt

195.1

1043 1390 629 60Nd

144.2

19

292

< $10/kg $10 - 100/kg $100 - 1000/kg $1000 - 10000/kg >$10000/kg 92U

238.0

93Np

238.0

71Lu

175.0

57La

138.9

slide-18
SLIDE 18
  • 2. Permanent Magnets
  • 2. Permanent Magnets
  • 2. Permanent Magnets
  • 2. Permanent Magnets -
  • Filling

Filling Filling Filling the Gap the Gap the Gap the Gap

slide-19
SLIDE 19

Tokyo, 21xi 2011

The permanent magnet market (~$10B) The permanent magnet market (~$10B)

SrFe12O1

9

Nd2Fe14 B

Ms = 0.38 MA m-1 K = 330 kJ m-3 TC = 740 K |BH|max< 35 MJm-3 Cost ~ 5$ kg-1 Ms = 1.28 MA m-1 K = 4.9 kJ m-3 TC = 588 K |BH|max< 400 MJm-3

K = sin2θ

θ

slide-20
SLIDE 20

Tokyo, 21xi 2011

Challenges Challenges

The 2 MA m-1 material. Find a usable soft material with M > 2 MAm-1 The megajoule magnet. Double |BH|MAX again to 1000 kJ m-3. The rare-earth free/reduced replacement of Nd-Fe-B. Should be as large as possible. Many applications depend on Ms

2

The gap magnet. Find a new material intermediate between ferrite and RE magnets.

slide-21
SLIDE 21

Tokyo, 21xi 2011

Soft magnets ≈ 10 B$ a-1

slide-22
SLIDE 22

Tokyo, 21xi 2011

Targets in the gap

|BH|MAX TC Ms K Raw materials cost kJm-3 K MAm-1 kJm-3 $/kg A 100 > 550 570 400 10 B 150 > 550 690 600 20 C 200 > 550 800 800 30

κ = (K/μ0Ms

2)1/2 > 1;

K > μ0Ms

2

Hc < Ha = 2K1/Ms

slide-23
SLIDE 23

Tokyo, 21xi 2011

Properties of some uniaxial ferromagnets

MnAl MnBi Mn2Ga Y2Fe14B Fe16N2 Fe3C YCo5 Ms (MA m

  • 1)

0.60 0.58 0.47 1.10 1.92 1.09 0.85 K1 (MJ m

  • 3)

1.7 0.90 2.35 1.1 1.0 0.45 6.5 TC (K) 650 628 >770 590 810 560 987 κ 1.95 1.46 2.35 0.85 0.43 0.55 2.7 Materials cost ($ kg

  • 1)

<10 < 20 > 100 < 30 < 10 < 10 <50

How do we find a suitable new material ? Combinatorial Materials Science

|BH|max 50 kJ m-3 Yamaguchi et al (89)

slide-24
SLIDE 24

Tokyo, 21xi 2011

Magnetocrystalline anisotropy Magnetocrystalline anisotropy

Shape anisotropy is limited to Ksh = ¼ μ0Ms

2(1- 3N ); it implies κ <½. A better source

is magnetocrystalline anisotropy, mainly due to spin-orbit coupling and the crystal-field interaction. Ea = K1 sin2θ + . . . . . The leading term in the crystal-field interaction is

Hcf = B2

0{3Jz 2 - J(J+1)}

B2

0 = A2 0 θ2

K1

cf ~ B2

0 J2. It varies as the electric field gradient x atomic quadrupole

moment Spin-orbit coupling is stronger for 4f than 3d atoms. Hence the use of rare-earth intermaetallics as permanent magnets.

slide-25
SLIDE 25

3. 3. 3.

  • 3. Perpendicular magnetic media

Perpendicular magnetic media Perpendicular magnetic media Perpendicular magnetic media and memory. and memory. and memory. and memory.

slide-26
SLIDE 26

Tokyo, 21xi 2011

Cost Cost Cost Cost -

  • the constraint

the constraint the constraint the constraint For bulk permanent magnets, we must choose elements which are easily available and cheap. 10 g for everyone on earth requires a million moles of magnet. This constraint does not apply for thin film devices. One mole is enough to provide everyone with a microchip containing a magnetic film a few nanometers thick.

slide-27
SLIDE 27

Tokyo, 21xi 2011

4 Be

9.01

12Mg

24.21

2 He

4.00

10Ne

20.18

24Cr

52.00

19K

38.21

11Na

22.99

3 Li

6.94

37Rb

85.47

55Cs

132.9

38Sr

87.62

56Ba

137.3

59Pr

140.9

1 H

1.00

5 B

10.81

9 F

19.00

17Cl

35.45

35Br

79.90

21Sc

44.96

22Ti

47.88

23V

50.94

26Fe

55.85

27Co

58.93

28Ni

58.69

29Cu

63.55

30Zn

65.39

31Ga

69.72

14Si

28.09

32Ge

72.61

33As

74.92

34Se

78.96

6 C

12.01

7 N

14.01

15P

30.97

16S

32.07

18Ar

39.95

39Y

88.91

40Zr

91.22

41Nb

92.91

42Mo

95.94

43Tc

97.9

44Ru

101.1

45Rh

102.4

46Pd

106.4

47Ag

107.9

48Cd

112.4

49In

114.8

50Sn

118.7

51Sb

121.8

52Te

127.6

53I

126.9

72Hf

178.5

73Ta

180.9

74W

183.8

75Re

186.2

76Os

190.2

77Ir

192.2

79Au

197.0

61Pm

145

70Yb

173.0

90Th

232.0

91Pa

231.0

87Fr

223

88Ra

226.0

89Ac

227.0

62Sm

150.4 105

66Dy

162.5 179 85

67Ho

164.9 132 20

68Er

167.3 85 20

58Ce

140.1

13 8 O

16.00 35

65Tb

158.9 229 221

64Gd

157.3

63Eu

152.0 90

66Dy

162.5 179 85

Atomic symbol Atomic Number Atomic weight Antiferromagnetic TN(K) Ferromagnetic TC(K)

Cost Periodic Table

80Hg

200.6

36Kr

83.80

54Xe

83.80

81Tl

204.4

82Pb

207.2

83Bi

209.0

84Po

209

85At

210

86Rn

222

Metal Radioactive Nonmetal BOLD Magnetic atom 25Mn

55.85 96

20Ca

40.08

13Al

26.98

69Tm

168.9 56

312 96

36

78Pt

195.1

1043 1390 629 60Nd

144.2

19

292

< $10/kg $10 - 100/kg $100 - 1000/kg $1000 - 10000/kg >$10000/kg 92U

238.0

93Np

238.0

71Lu

175.0

57La

138.9

slide-28
SLIDE 28

Tokyo, 21xi 2011 Af F1 Cu F2

AMR GMR TMR

1μm2 GMR TMR AMR

1 μm2

RAMAC 1955 40 Mb

~1010 bytes/year

HDD 2005 160 Gb

~1021 bytes/year

perpendicular

year caapcity platters size rpm 1955 40 Mb 50x2 24” 1200 2005 160 Gb 1 2.5” 18000

slide-29
SLIDE 29

Tokyo, 21xi 2011

Perpendicular thin film media and memory Perpendicular thin film media and memory

50 nm

Co-Cr-Pt-Ta-B

Next step – bit patterned media

af

I

planar magnetic tunnel junction (MTJ)

free pinned

B

slide-30
SLIDE 30

Tokyo, 21xi 2011

Thin film media and memory Thin film media and memory

Tetragonal L10 structure FePt FePd CoPt NiFe ? CoFe ?

slide-31
SLIDE 31

Tokyo, 21xi 2011

1.E-01 1.E+ 01 1.E+ 03 1.E+ 05 1.E+ 07 1.E+ 09 1.E+ 11 1E-05 0.001 0.1 10 1000 10000 1E+ 07

Crustal abundance (ppm) Annual production (t)

rare earths

Production/abundance Production/abundance

1 E 05

slide-32
SLIDE 32

Tokyo, 21xi 2011

Abundance/cost Abundance/cost

0.1 1 10 100 1000 10000 100000 0.001 0.1 10 1000 100000 Price ($/ mole) Abundance (ppm)

3d 4f

Fe Mn Co Ni Cr

slide-33
SLIDE 33

Tokyo, 21xi 2011

Gambling

G R E E N GREED

Science is sane. Physicists have saved space,time,energy Can they save the world ?

Versus

slide-34
SLIDE 34
  • 4. Summary and conclusions
  • 4. Summary and conclusions
  • 4. Summary and conclusions
  • 4. Summary and conclusions
slide-35
SLIDE 35

Tokyo, 21xi 2011

Summary Summary -

  • Where are the limits?

Where are the limits? Polarization μ0Ms 2.45 T improvement unlikely (bulk) Curie Temperature 1380 K improvement unlikely Anisotropy Field 40 T improvement pointless Energy product (BH)MAX512 kJ m-3 depends

  • n Ms,

Energy product (BH)max 475 kJ m-3 depends

  • n loop

shape

slide-36
SLIDE 36

Tokyo, 21xi 2011

Conclusions Conclusions

The era of exponential improvement of energy product is

  • ver.

Emergence of a new permanent magnet material superior to Nd2Fe14B is unlikely. Rare earths are overpriced; prices should fall as production increases, but Dy will remain problematic. Rare-earth free bulk magnets can be envisaged. Materials should be Fe or Mn based; >100 kJm-3 should be achievable, maybe 200 kJm-3 The challenge for two-phase hard/soft nanostructures is to align the hard nanoparticles. The megajoule magnet seems to out of reach Good prospects exist for new perpendicular thin films for magnetic recording or spin electronics.

slide-37
SLIDE 37

Tokyo, 21xi 2011