MICROSTRUCTURE OF MAGNETIC SUSPENSIONS STUDIED BY VIBRATING SHEARED SAMPLE MAGNETOMETRY

Magnetization measurements on suspensions, which are sheared during the measurements yield valuable information on their magnetic behaviour. This information can be interpreted in terms of the microstructure of the suspension. When shear and a magnetic field are applied during magnetization a dynamic process of network destruction, particle orientation and network formation takes place. This leads to a magnetic behaviour which depends on the relative amounts of particles and aggregates in the suspension. Measurements were performed on suspensions of CrO2 particles and Co doped gamma-Fe2O3 particles after various dispersing times, letdown and aging. The effect of the shear rate was studied at various magnetic field strengths. The measurements are interpreted in terms of single particles, (differently shaped and sized) aggregates and their mutual interactions (network formation). The effects of the spread of the magnetic moments and the varying shape and size of aggregates are discussed in relation to the interpretation of the measurements.