Relationship between median destructive field and remanent coercive forces for dispersed natural magnetite, titanomagnetite and hematite

Abstract

Remanent acquisition curves, remanent hysteresis curves and alternating field demagnetization curves were determined for a number of artificial rock specimens containing well-defined grain-size fractions between 5 and 250 µm of natural magnetite, titanomagnetite and hematite. From these curves, the remanent acquisition coercive force H′cr, the remanent coercive force Hcr and the median destructive field of IRM H½I were determined. Theoretically these parameters should be the same for an assembly of non-interacting, homogeneously distributed, randomly oriented single-domain grains. For a given hematite specimen H′cr, Hcr and H½I have about the same value in spite of the strong grain-size dependence of these parameters. For each specimen of magnetite and titanomagnetite the value of H′cr is larger than Hcr which again is larger than H½I. However, the ratios H′cr/Hcr and H½I/Hcr appear to have a (different) constant value. An interesting relationship which appears to hold for dispersed magnetite, titanomagnetite or hematite grains between 5 and 250 µm, independently of grain-size, quantity and packing density of the magnetic material, is: