Flux Instrument for Rapid Comparison of Crystal Anisotropies

A rotating disk instrument for rapid comparison of crystal anisotropies is described. In it a circular disk rotates in a magnetic field parallel to the place of the disk. Because of crystal anisotropy the magnetization I makes an angle θ with the magnetic intensity H. Some instruments, called torque magnetometers or magnetic torquemeters, measure the torque per unit volume, HI sinθ. In this instrument the disk rotates at 1800 rpm with its axis perpendicular to H. The changes in I sinθ, the component of the magnetization perpendicular to H, induce an emf in pickup coils, which are placed with their common axis perpendicular to the axis of the rotating disk and perpendicular to H. If the pickup coils are spherical, as in the similar instrument built by Siegel, the ratio of the flux through the coil to the magnetic moment of the specimen can be accurately calculated. Without such an absolute calibration the flux instrument is nevertheless convenient for rapidly comparing the disks of oriented polycrystalline silicon-iron with a single crystal disk of the same dimensions. The standard deviation between percent orientations (relative torque peaks) determined with this flux magnetometer and a conventional torque magnetometer is 3%. The emf from the pickup coils is integrated electronically and displayed on an oscilloscope.