A Home-built Vibrating Sample Magnetometer

This work presents the design and construction details of a computerized and fully automated vibrating sample magnetometer (VSM), one of the most commonly used instruments for measuring magnetic properties of materials. In this design, the sample to be analyzed is placed in a homogeneous magnetic field produced by an electromagnet which magnetizes the sample and vibrates it vertically between two pairs of pick-up coils. The vibrating sample could then be approximated to an oscillating point dipole and an electromotive force (emf) proportional to the magnetic moment of the sample is induced in the pick-up coils. The induced emf is amplified with a gain of 1000 and is converted into a digital signal by using an in-built analogue to digital converter module of a microcontroller. The magnetization field is varied by varying the supply voltage to the electromagnet and a microcontroller-operated power supply is used for this purpose. The voltage supplied to the electromagnet is also measured after digitization and RS232 standard serial data transmission technique is used to transmit the digitized data obtained from the microcontroller to the serial port of the computer. Computer software has been developed to receive data from the microcontroller and to plot the hysteresis (Magnetic induction field B verses magnetization field H) curve. Computer software was developed using Delphi 7 programming language. This software is capable of calculating some useful parameters related to the B-H curve. The VSM constructed in this work has been used successfully to obtain the B-H curve of an iron sample for preliminary testing and has proven its capability of producing B-H curves of other ferromagnetic samples. 1