Measurement of magnetic properties of cobalt-rare earth permanent magnets

Co-rare earth permanent magnets generally display a high intrinsic coercive force. In order to make magnetic measurements with such materials fully saturated, we have found it necessary to use magnetizing fields in excess of 50 kOe. The superconducting solenoid is ideally suited for generating such fields. In this study, we have used a 100 kOe Nb3-Sn superconducting solenoid for magnetizing samples and for measuring saturation magnetization. Demagnetization properties of long cylindrical samples have been measured in the superconducting solenoid, and also with a conventional hysteresigraph after the samples have been saturated with the superconducting solenoid or in some cases with a pulsed field solenoid. Short disk samples or ring magnets such as are used in traveling wave tube (TWT) designs are difficult to measure by these techniques. We have found torque magnetometry to be useful for such shapes. Open circuit magnetization is measured in this case. Results for ring magnets will be compared with peak axial field measurements for a periodic TWT structure. Reversible and irreversible changes in magnetization with temperature are also of interest. Techniques for measuring these changes are discussed.