Long term stability measurements on magnetic fluids

A scanning column magnetometer has been developed which can be used to observe small changes in the particle distribution in a magnetic fluid over a long period of time. This gives an insight into the behaviour of relatively stable magnetic fluids when they are subjected to long term treatment in a magnetic field or field gradient. A simple model is developed which can explain the features seen in the settling curves of the fluids but, because of the many unknown factors, cannot be used to give a full analysis of the results. A simple parameter is described which can be measured and can be used to compare the relative stabilities of different fluids.