GTBL042-18 GTBL042-Callister-v2 October 5, 2007 17:39
2nd Revise Page756 • Chapter 18 / Magnetic Properties18.2 (a)Explain the two sources of magnetic mo-
ments for electrons.
(b)Do all electrons have a net magnetic mo-
ment? Why or why not?
(c)Do all atoms have a net magnetic mo-
ment? Why or why not?
Diamagnetism and Paramagnetism
Ferromagnetism
18.3The magnetization within a bar of some metal
alloy is 1.2× 106 A/m at anHfield of 200
A/m. Compute the following:(a)the mag-
netic susceptibility,(b)the permeability, and
(c)the magnetic flux density within this ma-
terial.(d)What type(s) of magnetism would
you suggest as being displayed by this mate-
rial? Why?
18.4Confirm that there are 1.72 Bohr magne-
tons associated with each cobalt atom, given
that the saturation magnetization is 1.45×
106 A/m, that cobalt has an HCP crystal struc-
ture with an atomic radius of 0.1253 nm and
ac/aratio of 1.623.
18.5Assume there exists some hypothetical metal
that exhibits ferromagnetic behavior and that
has (1) a simple cubic crystal structure (Fig-
ure 3.42), (2) an atomic radius of 0.125 nm,
and (3) a saturation flux density of 0.85 tesla.
Determine the number of Bohr magnetons
per atom for this material.Antiferromagnetism and Ferrimagnetism
18.6Estimate(a)the saturation magnetization,
and(b)the saturation flux density of cobalt
ferrite [(CoFe 2 O 4 ) 8 ], which has a unit cell
edge length of 0.838 nm.
18.7The formula for samarium iron garnet
(Sm 3 Fe 5 O 12 ) may be written in the form
Smc 3 Fea 2 Fed 3 O 12 , where the superscriptsa,c,
anddrepresent different sites on which the
Sm^3 + and Fe^3 + ions are located. The spin
magnetic moments for the Sm^3 +and Fe^3 +
ions positioned in theaandcsites are ori-
ented parallel to one another and antipar-
allel to the Fe^3 + ions indsites. Compute
the number of Bohr magnetons associated
with each Sm^3 +ion, given the following in-
formation: (1) each unit cell consists of eight
formula (Sm 3 Fe 5 O 12 ) units; (2) the unit cell
is cubic with an edge length of 1.2529 nm;(3) the saturation magnetization for this ma-
terial is 1.35× 105 A/m; and (4) assume that
there are 5 Bohr magnetons associated with
each Fe^3 +ion.
Domains and Hysteresis
18.8Briefly describe the phenomenon of mag-
netic hysteresis, and why it occurs for ferro-
magnetic and ferrimagnetic materials.
18.9A ferromagnetic material has a remanence of
1.0 tesla and a coercivity of 15,000 A/m. Satu-
ration is achieved at a magnetic field strength
of 25,000 A/m, at which the flux density is
1.25 teslas. Using these data, sketch the entire
hysteresis curve in the rangeH=−25,000 to
+25,000 A/m. Be sure to scale and label both
coordinate axes.
18.10The following data are for a plain carbon steel
alloy:BB
H(A/m)(teslas) H(A/m)(teslas)
0 0 80 0.90
15 0.007 100 1.14
30 0.033 150 1.34
50 0.10 200 1.41
60 0.30 300 1.48
70 0.63(a)Construct a graph ofBversusH.
(b)What are the values of the initial perme-
ability and initial relative permeability?
(c)What is the value of the maximum per-
meability?
(d)At about whatHfield does this maximum
permeability occur?
(e)To what magnetic susceptibility does this
maximum permeability correspond?
18.11A bar of an iron–silicon alloy having theB–
Hbehavior shown in Figure 18.29 is inserted
within a coil of wire 0.40 m long and having
50 turns, through which passes a current of
0.1 A.
(a)What is theBfield within this bar?
(b)At this magnetic field,
(i)What is the permeability?
(ii)What is the relative permeability?
(iii)What is the susceptibility?
(iv)What is the magnetization?