Magnetization in a rod bent into a torus

[benf.stokes]

Homework Statement

I can't figure out why there is no bound current in the problem 6 (very subtle hint boldfaced) is the pdf below:
http://astronomy.mnstate.edu/cabanela/classes/phys370/homework/ps10.pdf

Can anybody give me a hint as to why there should be no bound current

The Attempt at a Solution

I know that the total dipole moment contained in a volume element must be constant. However i can't turn this into a relationship between the new M and the old one

 

[TSny]

See if you can follow the hint. How would the mass density ρ in the bent rod vary with radial distance s? See attached picture. Let point a be a point where the density happens to be the same as the unbent rod (ρ_o). Can you express the density ρ at an arbitrary point b in terms of the density ρ_o at a and the radial distances s and s_o?

If you can figure that out, then you should be able to see how the magnetization M varies with s.

 

[benf.stokes]

I figured it out due to your help. Thanks :)