Magnetic interactions in native horse spleen ferritin below the superparamagnetic blocking temperature

The magnetic interactions in a freeze-dried native horse spleen ferritin were quantified by measuring 5 K IRM and DCD remanence curves using a SQUID magnetometer, irreversible and reversible components of magnetic moment were determined for a range of fields to +/-30 kOe and attributed to blocked and unblocked SPM particles, respectively. This separation allowed the proportion and mean magnetic properties of each population to be determined. By fitting to a modified Langevin, the mean magnetic moment per particle of the unblocked population was calculated to be 15 mu(B), whilst constituting 67% of the magnetic moment at 5 K. Inter-particle interactions in ferritin were quantified using Henkel and Delta I plots, showing that ferritin particles weakly interact, with Delta I < 3%. This finding is consistent with a weak dipole-dipole interaction between otherwise magnetically independent particles. (C) 1998 Elsevier Science B.V. All rights reserved.