Maurain found that the outer layers of nickel were more magnetic than the inner ones. N. H. Williams said this must lead to an increased induction in a nickel rod if it were cut into a number of sections. He found that transverse sections did increase the induction for strong fields but lowered it for weak. This paper shows that because of this effect a bundle of nickel plates will orient itself in a magnetic field differently for weak fields than for strong. A possible explanation lies in the readiness which the elementary magnets of nickel have to align themselves with a magnetizing force, particularly those in the outer layers which are not affected so much by the mutual directive forces of the elementary magnets. The increase in permeability due to mechanically sectioning nickel bars seems to indicate that somewhat analogous conditions are produced when the permeability of a substance is increased by heat treatment.
S. R. WILLIAMS, "THE EFFECT OF TRANSVERSE JOINTS ON THE MAGNETIC INDUCTION IN NICKEL," J. Opt. Soc. Am. 10, 109-118 (1925)