Frequency independence of low-field magnetic susceptibility of rocks

A mutual inductance bridge with very low stray capacities has been used to seek, unsuccessfully, a frequency variation in the magnetic susceptibilities of rocks and dispersed powdered magnetite in low fields. The upper limit of susceptibility variation for the more strongly magnetic samples is 0.1% over the range 100 to 1000 Hz, smaller by a factor 10 than an estimate based on the theory of magnetic viscosity. Susceptibility anisotropy due to domain alignment is also independent of frequency.