Two questions came to my mind about Sec. 29.5 of Tipler (4th ed),
which is a lengthy optional topic entitled "Magnetism in Matter." If
you have the text, perhaps you can help me out.
(1) Curie's law for a paramagnetic material is given in Eq. (29.33).
I don't think the factor of 1/3 belongs. We expect a hyperbolic
tangent function, and tanh(x) = x for small x, not x/3. Perhaps the
1/3 was erroneously carried over from the term in the Langevin
expression g^2*J(J+1)/3. (Eg. see Kittel's Solid State Physics, 7th
ed, Eq. 22 in Chap. 14.) But with a Lande factor g=2 and spin J=1/2,
this term equals 1.
(2) There appears to be an inverse correlation in Table 29.2 between
the saturation magnetization (M_s) and the maximum value of the
relative permeability (K_m,max) of ferromagnetic materials. Is this a
coincidence? I think that K_m,max is the slope of Fig. 19.25 near
point c, and has to do with reorienting individual moments in
opposition to the exchange force rather than with moving domain
walls. OTOH, I think M_s is determined by the number of unpaired
electrons per atom (in accord with the Remark at the top of p. 908).
Why should these two things be inversely related?
--
Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5026
mungan@usna.edu http://physics.usna.edu/physics/faculty/mungan/