A general description based on the sensitivity function is presented for the effects of detection coil geometry and sample geometry on the output of a vibrating sample magnetometer (VSM). This function gives the VSM output versus position of a vibrating dipole. Calculations of the sensitivity function for axial and transverse detection coil configurations are presented using exact results and approximations including a spherical harmonic expansion. For axial, thick, rectangular cross‐section coils, the design yielding the output with a minimum sensitivity to sample position, sample shape, and sample size is presented. For the transverse geometry the small coil approximation is used. Various designs yielding maximum output and output insensitive to variations of sample geometry are reviewed. The signal‐to‐noise for various coil configurations is also discussed. Corrections for the VSM output are calculated for ’’large’’ samples with regular geometries (thin rod, circular cylinder, cube, and rectangular parallelepiped). The calculations were verified experimentally for a rod‐like sample for different orientations. The effects of applied field homogeneity, sample position errors, and sample support contributions are also discussed. Finally, applications of the analysis to other types of induction and force type magnetometers are discussed briefly.

Detection coil, sensitivity function, and sample geometry effects for vibrating sample magnetometers

On its 40th anniversary, I describe how the vibrating sample magnetometer (VSM) was developed and, later, how the very low frequency VSM, a flux‐integration device, was developed The important features of the moving sample technique, detection coil symmetry, calibration, sensitivity, and image effects are discussed briefly Some VSM adaptations discussed include operation at 3He and dilution refrigerator temperatures, at high hydrostatic pressures, in superconducting, high‐power water‐cooled and hybrid magnets, for very low frequency ac susceptibility, and with SQUID detectors

The vibrating sample magnetometer: Experiences of a volunteer (invited)

A general theory of a vibrating magnetometer pick-up system employing extended circular coils is outlined in the point magnetic dipole approximation Systems based upon cylindrical and toroidal coils are discussed in more detail with some attention focused on the ability of the systems to measure simultaneously all components of the magnetic moment The EMF detectability limits due to overall sensitivity, thermal noise and sample displacement are analysed for several existing and proposed coil arrangements A Smith-type arrangement has been found which is very stable with respect to axial displacement The tables essential for the rapid computation of the vectorial geometry factor (VGF) for arrangements composed of cylindrical coils have been compiled

https://iopscience.iop.org/article/10.1088/0022-3735/17/2/016/pdf

General theory of a vibrating magnetometer with extended coils

We here present a simple model of a vibrating sample magnetometer (VSM). The system allows recording magnetization curves at room temperature with a resolution of the order of 0.01 emu and is appropriated for macroscopic samples. The setup can be mounted with different configurations depending on the requirements of the sample to be measured (mass, saturation magnetization, saturation field, etc.). We also include here examples of curves obtained with our setup and comparison curves measured with a standard commercial VSM that confirms the reliability of our device.

/pdf/a-simple-vibrating-sample-magnetometer-for-macroscopic-2eczme90y4.pdf

A simple vibrating sample magnetometer for macroscopic samples.

A theoretical expression for the sensitivity of a detection coil for a vibrating sample magnetometer (VSM) is derived. This expression is used to design a detection coil system for a biaxial VSM for measuring the magnetization components in the direction of the applied field (x direction) and perpendicular to the applied field (y direction). This detection coil system is optimized with respect to the sensitivity, cross talk, and their position dependences. Both an eight‐coil detection system and a 12‐coil detection system are described. With the eight‐coil detection system, experiments have been performed showing that, in an electromagnet VSM, images contribute significantly to the measured signals. The 12‐coil configuration has the lowest position dependences and cross talk. An example shows that the average position dependences in the xy plane can be five times better compared to the eight‐coil configuration with comparable sensitivities. For both detection directions the signal varies less than 1% within a circle in the xy plane with a radius of 3 mm. For a displacement in the z direction and detection in the x direction the position dependence is larger (about 2% for a displacement of 3 mm). Finally, some examples demonstrate the usefulness of a biaxial VSM for the magnetic characterization of recording materials.

Design of a detection coil system for a biaxial vibrating sample magnetometer and some applications

The design of detection coil systems for use in vibrating sample magnetometers is discussed with particular reference to those magnetometers which are mounted on conventional iron cored magnets. Experimental results are presented for two distinct types of coil arrangements which can be fitted into a 2 in (5.1 cm) air gap. It is found that one of these coil arrangements possesses an extremely broad saddle point. For example, the equilibrium position of the vibrating sample can be displaced by +or-2.6 mm, +or-6.4 mm or 4.8 mm in the x, y or z directions without causing a change of more than 1% in the output voltage from the detection coils.

G J Bowden

Papers

Detection coil systems for vibrating sample magnetometers