About the Differential Sweep Method for Measuring of Ferrocolloids Magnetization Curves

Purpose. Justification and description of a laboratory method for measuring static magnetization curves specialized for ferrocolloids.
Methods. The measurement method is based on the paramagnetism of magnetic colloids and the quasi-linear response of their magnetisation to small perturbations of the external magnetic field. To obtain the magnetisation curve, the studying ferrocolloid sample is placed in a constant homogeneous field of a laboratory electromagnet with an iron core. By low-frequency modulation of the current in the coils of the electromagnet, a co-directional perturbation is applied to the constant field. Information about the response of the sample to the external field perturbation - the differential magnetic susceptibility of ferrocolloid - is extracted by electrical measurements. These measurements are carried out using a classical compensation device of two counter-connected wire coils, one of which contains the investigated sample. Conducting (sweeping) the measurements in a wide range of applied fields allows to collect a sequence of experimental values of differential susceptibility from which the desired magnetisation curve is reconstructed by numerical integration.
Results. The experimental setup for measuring the magnetisation curves of ferrocolloids was assembled. A theoretical description of the compensating electrical measuring device of the setup was proposed. The adjustment of the electrical scheme was carried out within several series of calibration experiments aimed at establishing the material parameters of the setup that were unknown from the theory. On the example of ferrocolloid of the type “magnetite - kerosene – oleic acid” both the process of obtaining primary experimental data and their subsequent processing, including the procedure of numerical integration, were demonstrated. It is established that the use of integration methods of a higher accuracy allows reducing the number of required experimental points and accelerating the measurement process without reducing the quality of the obtained curves.
Conclusion: The method applicable for measuring the magnetisation curves of ferrocolloids by differential sweeping is described, substantiated and implemented using laboratory equipment.

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