resonance, the magnetization losses are increased dramatically.) However, when
considering the quality factor Q (the inverse of the energy loss, and an important
figure of merit for high-frequency composite materials) the situation is quite
different (see Figure 8.40).
The commercial cobalt/nickel ferrite showing Bloch wall resonance in a frequency
range beginning close to 10
7 Hz showed a dramatic decrease in the quality factor in
this frequency range. It is clear that, above 10
7 Hz, the exchange-coupled nanocomposites function better than the conventional materials. Furthermore, the
quality factor increases with increasing coating thickness although, as shown in
Figure 8.40, this is correlated with a significant loss of susceptibility. Such an effect is
also apparent in the magnetization curves. Hence, when considering technical
applications the materials must be selected by making the best compromise between
frequency range, susceptibility, and losses.
References
1 Morup, S. and Christiansen, G. (1993)
J. Appl. Phys., 73, 6955–6957.
2 Jeong, J.-R., Lee, S.-L., and Shin, S.-C.
(2004) Phys. Stat. Sol., 241, 1593–1596.
3 Cullity, B.D. (1972) Introduction to Magnetic
Materials, Addison-Wesley, Reading, MA,
p. 410.
4 Kodama, R.H., Berkowitz, A.E., McNiff,
E.J., and Foner, S. (1997) J. Appl. Phys., 81,
5552–5557.
5 Tang, Z.X., Sorensen, C.M., Klabunde, K.J.,
and Hadjipanayis, G.C. (1991) Phys. Rev.
Lett., 67, 3602–3605.
6 Han, D.H., Wang, J.P., and Luo, H.L.
(1994) J. Magn. Magn. Mater., 136, 176–182.
7 Vollath, D. and Szab o, D.V. (2002) in
Innovative Processing of Films and
Nanocrystalline Powders (ed K.-L. Choy),
Imperial College Press, London,
pp. 219–251.
Figure 8.40 Quality factor (Q) of a soft
magnetic composite consisting of FeNi kernels
coated with SiO 2 of different thickness
compared to a commercially available (Co,Ni)
Fe 2 O 4 ferrite. While above a few 10
7 Hz the
conventional ferrite is no longer applicable, the
nanocomposite can be used up to frequencies
above 10
8 Hz, even when Q is reduced [24].
References j203
considering the quality factor Q (the inverse of the energy loss, and an important
figure of merit for high-frequency composite materials) the situation is quite
different (see Figure 8.40).
The commercial cobalt/nickel ferrite showing Bloch wall resonance in a frequency
range beginning close to 10
7 Hz showed a dramatic decrease in the quality factor in
this frequency range. It is clear that, above 10
7 Hz, the exchange-coupled nanocomposites function better than the conventional materials. Furthermore, the
quality factor increases with increasing coating thickness although, as shown in
Figure 8.40, this is correlated with a significant loss of susceptibility. Such an effect is
also apparent in the magnetization curves. Hence, when considering technical
applications the materials must be selected by making the best compromise between
frequency range, susceptibility, and losses.
References
1 Morup, S. and Christiansen, G. (1993)
J. Appl. Phys., 73, 6955–6957.
2 Jeong, J.-R., Lee, S.-L., and Shin, S.-C.
(2004) Phys. Stat. Sol., 241, 1593–1596.
3 Cullity, B.D. (1972) Introduction to Magnetic
Materials, Addison-Wesley, Reading, MA,
p. 410.
4 Kodama, R.H., Berkowitz, A.E., McNiff,
E.J., and Foner, S. (1997) J. Appl. Phys., 81,
5552–5557.
5 Tang, Z.X., Sorensen, C.M., Klabunde, K.J.,
and Hadjipanayis, G.C. (1991) Phys. Rev.
Lett., 67, 3602–3605.
6 Han, D.H., Wang, J.P., and Luo, H.L.
(1994) J. Magn. Magn. Mater., 136, 176–182.
7 Vollath, D. and Szab o, D.V. (2002) in
Innovative Processing of Films and
Nanocrystalline Powders (ed K.-L. Choy),
Imperial College Press, London,
pp. 219–251.
Figure 8.40 Quality factor (Q) of a soft
magnetic composite consisting of FeNi kernels
coated with SiO 2 of different thickness
compared to a commercially available (Co,Ni)
Fe 2 O 4 ferrite. While above a few 10
7 Hz the
conventional ferrite is no longer applicable, the
nanocomposite can be used up to frequencies
above 10
8 Hz, even when Q is reduced [24].
References j203