Altshuler et al discovered that dICO/dlnt, the rate of increase of the critical current
IC with time in
polycrystalline high TC
samples, traced a peak when measured versus
HM, the amplitude of the sweep of the flux trapping magnetic field. We show that the sharp peak in
dICO/dlnt
which their model generates arises from a special feature of the formulae they use to describe
IC
versus HM. Pursuing an extension of these formulae, and exploiting a Brandt–Indenbom
formula for the return field of the magnetized grains, we (i) reproduce
observations of Altshuler et al, Batista-Leyva et al and a family of curves of
dICO/dlnt
reported by Cobas et al, and (ii) estimate the return fields. We also explore the peak structure of
dICO/dlnt
versus HM
generated by using two well known empirical expressions for
IC(H), and the Brandt–Indenbom formula.