408
I. de Moraes and N. M. Dempsey
Table 17.1 Intrinsic properties of various soft magnetic and hard magnetic phases
Material
μ 0 M s (T)
μ 0 M s (emu/g)
K 1 (MJ/m 3 )
δ w (nm)
Soft magnetic phases
Co
1.81
161
0.410
24
Fe
2.15
218
0.048
64
Fe 65 Co 35
2.45
240
0.018
90
Fe 20 Ni 80
1.00
93
– 0.002
2000
Fe 3 Pt
1.83
125
– 0.4
15
Fe 3 O 4
0.63
92
– 0.013
73
Hard magnetic phases
Nd 2 Fe 14 B
1.61
171
4.9
3.9
SmCo 5
1.07
110
17.2
3.6
Sm 2 Co 17
1.25
120
3.3
10
CoFe 2 O 4
0.56
80
0.18
13
SrFe 12 O 19
0.48
71
0.35
14
BaFe 12 O 19
0.48
71
0.33
14
FePt
1.43
74
6.6
3.7
CoPt
1.00
50
4.9
5.0
Sm 2 Fe 17 N 3
1.54
157
8.6
3.7
FePd
1.41
114
1.7
10
FeNi (L1 0 )
1.6
154
1.0
–
Much effort has gone into fabricating hard-soft nanocomposite permanent
magnets using a range of processing techniques based on (a) bulk metallurgical
synthesis, (b) physical vapour deposition and (c) chemical synthesis. The bulk metallurgical synthesis route includes techniques already used in magnet fabrication (e.g.
melt spinning) and the mass production of amorphous materials (e.g. ball milling)
and could thus be considered a natural extension of today’s magnet manufacturing
industry. However, the maximum energy product of the attained hard-soft nanocomposites achieved to date is not better than that of single-phase magnets. This can
be attributed to the technical challenges faced in preparing textured materials, to
reach high remanence, with grain size below 10 nm, needed to reach coercivity in
excess of 1T. The physical vapour deposition route is only suitable for the fabrication of thin and thick films. On the one hand, films can serve as model systems
to study the link between micro/nanostructure and extrinsic magnetic properties in
nanocomposite materials [8]. On the other hand, there is huge potential for their use in
micro/nanosystems requiring high energy density but compact magnetic flux sources
[9]. In this chapter, we chose to focus our attention on the chemical synthesis of hardsoft nanocomposite permanent magnets, but before presenting cases studies from
literature, we will very briefly recall studies related to bulk metallurgical synthesis
and physical vapour deposition of hard/soft nanocomposites.
I. de Moraes and N. M. Dempsey
Table 17.1 Intrinsic properties of various soft magnetic and hard magnetic phases
Material
μ 0 M s (T)
μ 0 M s (emu/g)
K 1 (MJ/m 3 )
δ w (nm)
Soft magnetic phases
Co
1.81
161
0.410
24
Fe
2.15
218
0.048
64
Fe 65 Co 35
2.45
240
0.018
90
Fe 20 Ni 80
1.00
93
– 0.002
2000
Fe 3 Pt
1.83
125
– 0.4
15
Fe 3 O 4
0.63
92
– 0.013
73
Hard magnetic phases
Nd 2 Fe 14 B
1.61
171
4.9
3.9
SmCo 5
1.07
110
17.2
3.6
Sm 2 Co 17
1.25
120
3.3
10
CoFe 2 O 4
0.56
80
0.18
13
SrFe 12 O 19
0.48
71
0.35
14
BaFe 12 O 19
0.48
71
0.33
14
FePt
1.43
74
6.6
3.7
CoPt
1.00
50
4.9
5.0
Sm 2 Fe 17 N 3
1.54
157
8.6
3.7
FePd
1.41
114
1.7
10
FeNi (L1 0 )
1.6
154
1.0
–
Much effort has gone into fabricating hard-soft nanocomposite permanent
magnets using a range of processing techniques based on (a) bulk metallurgical
synthesis, (b) physical vapour deposition and (c) chemical synthesis. The bulk metallurgical synthesis route includes techniques already used in magnet fabrication (e.g.
melt spinning) and the mass production of amorphous materials (e.g. ball milling)
and could thus be considered a natural extension of today’s magnet manufacturing
industry. However, the maximum energy product of the attained hard-soft nanocomposites achieved to date is not better than that of single-phase magnets. This can
be attributed to the technical challenges faced in preparing textured materials, to
reach high remanence, with grain size below 10 nm, needed to reach coercivity in
excess of 1T. The physical vapour deposition route is only suitable for the fabrication of thin and thick films. On the one hand, films can serve as model systems
to study the link between micro/nanostructure and extrinsic magnetic properties in
nanocomposite materials [8]. On the other hand, there is huge potential for their use in
micro/nanosystems requiring high energy density but compact magnetic flux sources
[9]. In this chapter, we chose to focus our attention on the chemical synthesis of hardsoft nanocomposite permanent magnets, but before presenting cases studies from
literature, we will very briefly recall studies related to bulk metallurgical synthesis
and physical vapour deposition of hard/soft nanocomposites.