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

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

Revised Pages

758 • Chapter 18 / Magnetic Properties

Soft Magnetic Materials

Hard Magnetic Materials

18.13Assume the silicon–iron (97Fe, 3Si) in Table

18.5 just reaches the point of saturation when

inserted within the coil in Problem 18.1. Com-

pute the saturation magnetization.

18.14Figure 18.30 shows theB-versus-Hcurve for

a nickel–iron alloy.

(a)What is the saturation flux density?

(b)What is the saturation magnetization?

(c)What is the remanence?

(d)What is the coercivity?

(e)On the basis of data in Tables 18.5 and

18.6, would you classify this material as a

soft or hard magnetic material? Why?

Superconductivity

18.15For a superconducting material at a tempera-

tureTbelow the critical temperatureTC, the

critical fieldHC(T), depends on temperature

according to the relationship

HC(T)=HC(0)

(

1 −

T^2

TC^2

)

(18.14)

whereHC(0) is the critical field at 0 K.

(a)Using the data in Table 18.7, calculate the

critical magnetic fields for lead at 2.5 and

5.0 K.

(b)To what temperature must lead be cooled

in a magnetic field of 15,000 A/m for it to

be superconductive?

18.16Using Equation 18.14, determine which of

the superconducting elements in Table 18.7

are superconducting at 2 K and a magnetic

field of 40,000 A/m.

18.17Cite the primary limitation of the new su-

perconducting materials that have relatively

high critical temperatures.

DESIGN PROBLEM

Ferromagnetism

18.D1A cobalt–iron alloy is desired that has a sat-

uration magnetization of 1.47× 106 A/m.

Specify its composition in weight percent

iron. Cobalt has an HCP crystal structure

withc/aratio of 1.623. Assume that the unit

cell volume for this alloy is the same as for

pure Co.