Critical Materials for Magnetism · 6 Antiferromagnetism and other magnetic order 7 Micromagnetism 8 Nanoscale magnetism 9 Magnetic resonance 10 Experimental methods 11 Magnetic materials

Tokyo, 21xi 2011

J. M. D. Coey

Physics Department and CRANN, Trinity College Dublin 2, Ireland

www.tcd.ie/Physics/Magnetism

Critical Materials for MagnetismCritical Materials for Magnetism

1. Materials used for applications of magnetism

Permanent magnetsSoft magnetsMagnetic recording

2. Permanent magnets — filling the gap

3. Perpendicular magnetic media and memory

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

Tokyo, 21xi 2011

Critical raw materials Critical raw materials –– EU reportEU report

* Platinum group metals

Germanium

Tantalum

1.1. Materials used for applications Materials used for applications of magnetismof magnetism

Tokyo, 21xi 2011

4 Be9.01

2 + 2s0

12Mg24.21

2 + 3s0

2 He4.00

10Ne20.18

24Cr52.003 + 3d3

312

19K38.21

1 + 4s0

11Na22.99

1 + 3s0

3 Li6.94

1 + 2s0

37Rb85.47

1 + 5s0

55Cs13.29

1 + 6s0

38Sr87.622 + 5s0

56Ba137.32 + 6s0

59Pr140.93 + 4f2

1 H1.00

5 B10.81

9 F19.00

17Cl35.45

35Br79.90

21Sc44.963 + 3d0

22Ti47.884 + 3d0

23V50.943 + 3d2

26Fe55.853 + 3d5

1043

27Co58.932 + 3d7

1390

28Ni58.692 + 3d8

629

29Cu63.552 + 3d9

30Zn65.392 + 3d10

31Ga69.723 + 3d10

14Si28.09

32Ge72.61

33As74.92

34Se78.96

6 C12.01

7 N14.01

15P30.97

16S32.07

18Ar39.95

39Y88.912 + 4d0

40Zr91.224 + 4d0

41Nb92.915 + 4d0

42Mo95.945 + 4d1

43Tc97.9

44Ru101.13 + 4d5

45Rh102.43 + 4d6

46Pd106.42 + 4d8

47Ag107.91 + 4d10

48Cd112.42 + 4d10

49In114.83 + 4d10

50Sn118.74 + 4d10

51Sb121.8

52Te127.6

53I126.9

57La138.93 + 4f0

72Hf178.54 + 5d0

73Ta180.95 + 5d0

74W183.86 + 5d0

75Re186.24 + 5d3

76Os190.23 + 5d5

77Ir192.24 + 5d5

78Pt195.12 + 5d8

79Au197.01 + 5d10

61Pm145

70Yb173.03 + 4f13

71Lu175.03 + 4f14

90Th232.04 + 5f0

91Pa231.05 + 5f0

92U238.04 + 5f2

87Fr223

88Ra226.02 + 7s0

89Ac227.03 + 5f0 62Sm

150.43 + 4f5

105

66Dy162.53 + 4f9

179 85

67Ho164.93 + 4f10

132 20

68Er167.33 + 4f11

85 20

58Ce140.14 + 4f013

Ferromagnet TC > 290K

Antiferromagnet with TN > 290K

8 O16.00

35

65Tb158.93 + 4f8

229 221

64Gd157.3

3 + 4f7292

63Eu152.02 + 4f7

90

60Nd144.23 + 4f3

19

66Dy162.53 + 4f9

179 85

Atomic symbolAtomic Number

Typical ionic changeAtomic weight

Antiferromagnetic TN(K) Ferromagnetic TC(K)

Antiferromagnet/Ferromagnet with TN/TC < 290 KMetal

Radioactive

Magnetic Periodic Table

80Hg200.62 + 5d10

93Np238.05 + 5f2

94Pu244

95Am243

96Cm247

97Bk247

98Cf251

99Es252

100Fm257

101Md258

102No259

103Lr260

36Kr83.80

54Xe83.80

81Tl204.43 + 5d10

82Pb207.24 + 5d10

83Bi209.0

84Po209

85At210

86Rn222

Nonmetal Diamagnet

Paramagnet

BOLD Magnetic atom

25Mn55.852 + 3d5

96

20Ca40.082 + 4s0

13Al26.983 + 2p6

69Tm168.93 + 4f12

56

Tokyo, 21xi 2011

OSiAlFeMgCaKNaHOthers

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

HoEr

Tm

Yb

-1

0

1

2

3

4

5

Cr Mn Fe Co Ni Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb3d elements 4f elements

PmLog

(abu

ndan

ce, p

pm)

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

Tokyo, 21xi 2011

HysteresisHysteresis

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

M (Am-1)

H (Am-

1)

Ms

Mr

Hd

working point

coercivityHc

Tokyo, 21xi 2011

The demagnetizing fieldThe demagnetizing field

M BHN

S

∇B = 0

B = μ0(H + M)Stray field

Demagnetizing field

Hd ≈ -N M

demagnetizing factor 0 ≤N ≤ 1

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-CoNd-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

HardMagnets

MagneticRecording

Hard Magnets

Fe, Sr, Ba, Nd, Sm, Co, Dy, Zr

Soft Magnets

Fe, SI, Co, Ni, Zn, Mn

Magnetic Recording

Fe, Ni, Co, Ta, PtBreakdown of magnetic materials in 2000 - 30 B$

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

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,AlSm-Co; Sm, Co, Fe,

Zr,Cu

SrFe12O19

Nd2Fe14B

Nd,Dy,Tb,Fe,Co,B

Tokyo, 21xi 2011

The LimitsThe 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

Tokyo, 21xi 2011




2


2



Magnetic ordering temperature of > 2000 materials

αFe2O3 Fe Co

Magnetic ordering temperature (K)

Highest Néel temperature

Highest Curie temperature

Tokyo, 21xi 2011




2


2

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


Slater-Pauling Curve

Slope -1m μB

Fe65Co35 Ms =1.95 MAm-1

Cr Mn Fe Co Ni Cu6 7 8 9 10 11

Valence electrons

Tokyo, 21xi 2011




2


2



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

Tokyo, 21xi 2011




2


2



The main achievement of technical magnetism in the 20th century was mastery of coercivity 1900: 103 < Hc < 105 A m-1

2000: 1 < Hc < 2 107 A m-1

Tokyo, 21xi 2011

4 Be9.01

12Mg24.21

2 He4.00

10Ne20.18

24Cr52.00

19K38.21

11Na22.99

3 Li6.94

37Rb85.47

55Cs132.9

38Sr87.62

56Ba137.3

59Pr140.9

1 H1.00

5 B10.81

9 F19.00

17Cl35.45

35Br79.90

21Sc44.96

22Ti47.88

23V50.94

26Fe55.85

27Co58.93

28Ni58.69

29Cu63.55

30Zn65.39

31Ga69.72

14Si28.09

32Ge72.61

33As74.92

34Se78.96

6 C12.01

7 N14.01

15P30.97

16S32.07

18Ar39.95

39Y88.91

40Zr91.22

41Nb92.91

42Mo95.94

43Tc97.9

44Ru101.1

45Rh102.4

46Pd106.4

47Ag107.9

48Cd112.4

49In114.8

50Sn118.7

51Sb121.8

52Te127.6

53I126.9

72Hf178.5

73Ta180.9

74W183.8

75Re186.2

76Os190.2

77Ir192.2

79Au197.0

61Pm145

70Yb173.0

90Th232.0

91Pa231.0

87Fr223

88Ra226.0

89Ac227.0

62Sm150.4

105

66Dy162.5

179 85

67Ho164.9

132 20

68Er167.3

85 20

58Ce140.1

13

8 O16.00

35

65Tb158.9

229 221

64Gd157.3

63Eu152.0

90

66Dy162.5

179 85


Atomic weight


Cost Periodic Table

80Hg200.6

36Kr83.80

54Xe83.80

81Tl204.4

82Pb207.2

83Bi209.0

84Po209

85At210

86Rn222

Metal

Radioactive

Nonmetal

BOLD Magnetic atom

25Mn55.85

96

20Ca40.08

13Al26.98

69Tm168.9

56

312 96

36

78Pt195.1

1043 1390 629

60Nd144.2

19 292

< $10/kg$10 - 100/kg

$100 - 1000/kg$1000 - 10000/kg

>$10000/kg

92U238.0

93Np238.0

71Lu175.0

57La138.9

2. Permanent Magnets 2. Permanent Magnets -- Filling Filling the Gap the Gap

Tokyo, 21xi 2011

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

SrFe12O19

Nd2Fe14B

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

Tokyo, 21xi 2011

ChallengesChallenges

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.

Tokyo, 21xi 2011

Soft magnets ≈ 10 B$ a-1

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/μ0Ms2)1/2 > 1;

K > μ0Ms2

Hc < Ha = 2K1/Ms

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)

Tokyo, 21xi 2011

Magnetocrystalline anisotropyMagnetocrystalline anisotropy

Shape anisotropy is limited to Ksh = ¼ μ0Ms2(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 = B20{3Jz

2 - J(J+1)} B20 = A2

0 θ2

K1cf ~ 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.

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

Tokyo, 21xi 2011

Cost Cost -- the constraintthe 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.

Tokyo, 21xi 2011

4 Be9.01

12Mg24.21

2 He4.00

10Ne20.18

24Cr52.00

19K38.21

11Na22.99

3 Li6.94

37Rb85.47

55Cs132.9

38Sr87.62

56Ba137.3

59Pr140.9

1 H1.00

5 B10.81

9 F19.00

17Cl35.45

35Br79.90

21Sc44.96

22Ti47.88

23V50.94

26Fe55.85

27Co58.93

28Ni58.69

29Cu63.55

30Zn65.39

31Ga69.72

14Si28.09

32Ge72.61

33As74.92

34Se78.96

6 C12.01

7 N14.01

15P30.97

16S32.07

18Ar39.95

39Y88.91

40Zr91.22

41Nb92.91

42Mo95.94

43Tc97.9

44Ru101.1

45Rh102.4

46Pd106.4

47Ag107.9

48Cd112.4

49In114.8

50Sn118.7

51Sb121.8

52Te127.6

53I126.9

72Hf178.5

73Ta180.9

74W183.8

75Re186.2

76Os190.2

77Ir192.2

79Au197.0

61Pm145

70Yb173.0

90Th232.0

91Pa231.0

87Fr223

88Ra226.0

89Ac227.0

62Sm150.4

105

66Dy162.5

179 85

67Ho164.9

132 20

68Er167.3

85 20

58Ce140.1

13

8 O16.00

35

65Tb158.9

229 221

64Gd157.3

63Eu152.0

90

66Dy162.5

179 85


Atomic weight


Cost Periodic Table

80Hg200.6

36Kr83.80

54Xe83.80

81Tl204.4

82Pb207.2

83Bi209.0

84Po209

85At210

86Rn222

Metal

Radioactive

Nonmetal

BOLD Magnetic atom

25Mn55.85

96

20Ca40.08

13Al26.98

69Tm168.9

56

312 96

36

78Pt195.1

1043 1390 629

60Nd144.2

19 292

< $10/kg$10 - 100/kg

$100 - 1000/kg$1000 - 10000/kg

>$10000/kg

92U238.0

93Np238.0

71Lu175.0

57La138.9

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

Tokyo, 21xi 2011

Perpendicular thin film media and memoryPerpendicular thin film media and memory

50 nm

Co-Cr-Pt-Ta-B

Next step – bit patterned mediaaf

I

planar magnetic tunnel junction (MTJ)

free

pinned

B

Tokyo, 21xi 2011

Thin film media and memoryThin film media and memory

Tetragonal L10 structure

FePtFePdCoPtNiFe ?CoFe ?

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 100000

1E+070Crustal abundance (ppm)

Ann

ual p

rodu

ctio

n (t)

rare earths

Production/abundanceProduction/abundance

1 E 05

Tokyo, 21xi 2011

Abundance/costAbundance/cost

0.1

1

10

100

1000

10000

100000

0.001 0.1 10 1000 100000Price ($/mole)

Abundan

ce (

ppm

) 3d

4f

Fe

Mn

Co

NiCr

Tokyo, 21xi 2011

Gambling

GREENGREED

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

Versus

4. Summary and conclusions4. Summary and conclusions

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 Timprovement pointlessEnergy product (BH)MAX512 kJ m-3 depends on Ms,

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

Tokyo, 21xi 2011

ConclusionsConclusions

The era of exponential improvement of energy product is over.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 reachGood prospects exist for new perpendicular thin films for magnetic recording or spin electronics.

Tokyo, 21xi 2011

Documents

Critical Materials for Magnetism · 6 Antiferromagnetism and other magnetic order 7 Micromagnetism 8 Nanoscale magnetism 9 Magnetic resonance 10 Experimental methods 11 Magnetic materials