THE POWER-LAW DECAY OF A COLLECTIVE DIPOLE WITH CYCLE NUMBER IN ROTATIONAL HYSTERESIS OF MAGNETIC RECORDING MEDIA

A collective dipole is written into a section of magnetic recording ta pe containing metal particles. The section is then rotated in a magnet ic field to follow the decay with cycle number n of the dipole moment mu(n). The dipole decays as mu(n) = mu(infinity) - Delta mu n(-p) with small values of p < 0.2 in fields near the coercivity. The measuremen ts of changes within each cycle are interpreted in terms of the revers als of a fraction f(s) of the particles. Most of those switch twice pe r cycle, but some depart from the fraction f(+) that remain in the sen se of the original dipole to join the growing fraction f(-) that remai n in the opposite sense. These fractions are extracted from the data a nd followed from cycle to cycle for thousands of cycles. It is suggest ed that magnetic recording tapes could he used to study self-organized criticality.