DESIGN OF A DETECTION COIL SYSTEM FOR A BIAXIAL VIBRATING SAMPLE MAGNETOMETER AND SOME APPLICATIONS

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.