Metrological analysis of a magnetometer to measure the magnetization of magnetic nanofluids in strong magnetic fields

The successful application of magnetic nanofluids requires magnetometric instruments for studying their magnetization processes. The paper proposes a design of a mobile magnetometer with Hall sensors, which made it possible to take into account the features of the physical and mechanical properties of a wide range of laboratory and industrial magnetic nanofluids. Permanent magnets made of SmCo₅ alloy and magnetic cores made of soft magnetic steel form the device magnetic circuit. Magnetic fluxes add up in a magnetic fluid area and create a uniform field with an intensity up to (2 ÷ 4) ⋅ 10⁵ A/m. The magnetizing magnetic field intensity and the value of the magnetic field induction in a nanofluid are measured using Hall effect transducers, which are connected oppositely in a single measuring electrical circuit to determine the Hall EMF of the proportional magnetization of the material under study. A circuit method for correcting the non-equipotentiality EMF is used to improve the measurement accuracy. A comparative estimate of the relative error in measuring the magnetization of magnetic nanofluids was less than 2 %. It has been established that the magnetometer methodological error is due to the fact that Hall effect transducers do not reflect the field in the substance correctly due to non-magnetic gaps. The device methodical error was estimated by numerical simulation of the magnetic field parameters in a real magnetic system of the MDM-P1 device using the Elcut computer program. Based on the results of a numerical analysis of the device magnetic system model, we have found the dependences of the methodological error in measuring the induction of the magnetic field in the substance and the magnetizing field intensity on the size of non-magnetic cavities in the device magnetic circuit and the magnetic properties of the materials under study. It is shown that the relative methodological error in determining the magnetization of magnetic nanofluids on the MDM-P1 device does not exceed 1 %.