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

GTBL042-18 GTBL042-Callister-v2 September 13, 2007 13:46

Revised Pages

740 • Chapter 18 / Magnetic Properties

Concept Check 18.4

Schematically sketch on a single plot theB-versus-Hbehavior for a ferromagnetic

material (a) at 0 K, (b) at a temperature just below its Curie temperature, and

(c) at a temperature just above its Curie temperature. Briefly explain why these

curves have different shapes.

[The answer may be found at http://www.wiley.com/college/callister (Student Companion Site).]

Concept Check 18.5

Schematically sketch the hysteresis behavior for a ferromagnet which is gradually

demagnetized by cycling in anHfield that alternates direction and decreases in

magnitude.

[The answer may be found at http://www.wiley.com/college/callister (Student Companion Site).]

18.8 MAGNETIC ANISOTROPY

The magnetic hysteresis curves discussed in the previous section will have different

shapes depending on various factors: (1) whether the specimen is a single crystal or

polycrystalline; (2) if polycrystalline, any preferred orientation of the grains; (3) the

presence of pores or second-phase particles; and (4) other factors such as temperature

and, if a mechanical stress is applied, the stress state.

For example, theB(orM) versusHcurve for a single crystal of a ferromagnetic

material depends on its crystallographic orientation relative to the direction of the

appliedHfield. This behavior is demonstrated in Figure 18.17 for single crystals

of nickel (FCC) and iron (BCC), where the magnetizing field is applied in [100],

[110], and [111] crystallographic directions; and in Figure 18.18 for cobalt (HCP)

2.0

1.0

0

Magnetization,

M

(10

6 A/m)

0 10,000 20,000 30,000 40,000 50,000

Magnetic field strength, H (A/m)

[100]

[110]

[111]

[111]

[110] [100]

Iron

A B C Nickel

Figure 18.17

Magnetization curves for

single crystals of iron and

nickel. For both metals, a

different curve was

generated when the

magnetic field was applied

in each of [100], [110], and

[111] crystallographic

directions. [Adapted from

K. Honda and S. Kaya, “On

the Magnetisation of Single

Crystals of Iron,”Sci. Rep.

Tohoku Univ.,15, 721

(1926); and from S. Kaya,

“On the Magnetisation of

Single Crystals of Nickel,”

Sci. Rep. Tohoku Univ.,17,

639 (1928).]