GTBL042-18 GTBL042-Callister-v2 September 13, 2007 13:46
Revised Pages18.9 Soft Magnetic Materials • 741Magnetization,M
(106 A/m)Magnetic field strength, H (10^6 A/m)1.51.00.5(^00) 0.2 0.4 0.6 0.8
[0001]
[1010], [0001]
[1120]
[1010]
[1120]
Figure 18.18
Magnetization curves for
single crystals of cobalt. The
curves were generated when
the magnetic field was
applied in [0001] and
[1010]/[1120]
crystallographic directions.
[Adapted from S. Kaya, “On
the Magnetisation of Single
Crystals of Cobalt,”Sci. Rep.
Tohoku Univ.,17, 1157
(1928).]
in [0001] and [1010]/[1120] directions. This dependence of magnetic behavior on
crystallographic orientation is termedmagnetic(or sometimesmagnetocrystalline)
anisotropy.
For each of these materials there is one crystallographic direction in which mag-
netization is easiest—that is, saturation (ofM) is achieved at the lowestHfield;
this is termed a direction ofeasy magnetization.For example, for Ni (Figure 18.17)
this direction is [111] inasmuch as saturation occurs at point A; whereas, for [110]
and [100] orientations, saturation points correspond, respectively, to points B and C.
Correspondingly, easy magnetization directions for Fe and Co are [100] and [0001],
respectively (Figures 18.17 and 18.18). Conversely, ahardcrystallographic direction
is that direction for which saturation magnetization is most difficult; hard directions
for Ni, Fe, and Co are [100], [111], and [1010]/[1120].
As noted in the previous section, the insets of Figure 18.13 represent domain
configurations at various stages along theB(orM) versusHcurve during the mag-
netization of a ferromagnetic/ferrimagnetic material. Here, each of the arrows repre-
sents a domain’s direction of easy magnetization; domains whose directions of easy
magnetization are most closely aligned with theHfield grow, at the expense of the
other domains that shrink (insets V through X). Furthermore, the magnetization of
the single domain in inset Y also corresponds to an easy direction. And saturation
is achieved as the direction of this domain rotates away from the easy direction into
the direction of the applied field (inset Z).
18.9 SOFT MAGNETIC MATERIALS
The size and shape of the hysteresis curve for ferromagnetic and ferrimagnetic ma-
terials is of considerable practical importance. The area within a loop represents a
magnetic energy loss per unit volume of material per magnetization–demagnetization
cycle; this energy loss is manifested as heat that is generated within the magnetic
specimen and is capable of raising its temperature.
Both ferromagnetic and ferrimagnetic materials are classified as eithersoftor
soft magnetic hardon the basis of their hysteresis characteristics.Soft magnetic materialsare used
material in devices that are subjected to alternating magnetic fields and in which energy losses