Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

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Revised Pages

18.7 Domains and Hysteresis • 739

B

M N

P

H

L

Figure 18.15 A hysteresis curve at less than

saturation (curveNP) within the saturation

loop for a ferromagnetic material. TheB–H

behavior for field reversal at other than

saturation is indicated by curveLM.

reversed to zero. One method of demagnetizing a ferromagnet or ferrimagnet is to

repeatedly cycle it in anHfield that alternates direction and decreases in magnitude.

At this point it is instructive to compare theB-versus-Hbehaviors of param-

agnetic, diamagnetic, and ferromagnetic/ferrimagnetic materials; such a comparison

is shown in Figure 18.16. The linearity of paramagnetic and diamagnetic materials

may be noted in the small inset plot, whereas the behavior of a typical ferromag-

netic/ferrimagnetic is nonlinear. Furthermore, the rationale for labeling paramag-

netics and diamagnetics as nonmagnetic materials is verified by comparing theB

scales on the vertical axes of the two plots—at anHfield strength of 50 A/m, the fer-

romagnetic/ferrimagnetic materials flux density is on the order of 1.5 tesla, whereas

for the paramagnetic and diamagnetic materials it is on the order of 5× 10 −^5 tesla.

1.5

1

0.5

(^002550)
0 25 50
Flux density,
B (tesla)
Ferromagnetic and
ferrimagnetic
Magnetic field strength, H (A/m)
1 × 10 ^4
5 × 10 ^5
0
Diamagnetic and
paramagnetic
Figure 18.16 Comparison
ofB-versus-Hbehaviors
for ferromagnetic/
ferrimagnetic and
diamagnetic/paramagnetic
materials (inset plot). Here
it may be noted that
extremely smallBfields are
generated in materials that
experience only
diamagnetic/paramagnetic
behavior, which is why they
are considered to be
nonmagnetics.