An infinitely long cylinder, of radius R, carries a frozen-in magnetisation, parallel to the z-axis, M=ks k-hat, where k is a constant and s is the distance from the axis. There is no free current anywhere. Find the magnetic field B inside and outside the cylinder by two different methods:
i) Locate all bound currents, and calculate the field they produce; and
ii) Use Ampere's law, the loop integral of H.dl=I(subscript enc), to find H, then get Bfrom H=(1/mu0)B-M
The Attempt at a Solution
I found the answer on http://www.nhn.ou.edu/~shaferry/41832005_files/finalsol.pdf
but what I don't understand is why far away from the loop the B field must go to zero. I would be grateful if someone could explain please.