Magnetization time decay in particulate media

We report on magnetization time decay data on several commercial and experimental tapes (γ-Fe
2
O
3
, Co-doped, and Co-Cr) measured at room temperature between 1s and 10
⁴
s. We found that the decay of the magnetization with time does not follow a simple log t relation. We analyze our data with an empirical model which allows one to relate values of coercive field, H
c
, obtained with a 60 Hz B-H looper, to that measured with a slow VSM field cycle. The methodology we have developed appears to have promise as a means of correlating data over ten orders of magnitude of time from 10
^-6
s to 10
⁴
s.