Astroid plotter for thin magnetic films

The rotational astroid of uniaxial thin films may be obtained from the cross-field loop graphically or electronically by assuming Slenczewski\´s tangent rule. The graphical construction by means of the tangent rule is demonstrated. The derivation of the transformation to obtain the astroid electronically is given, and a comparison is made with astroids obtained graphically as well as those obtained by direct static measurements. An astroid plotter has been constructed using standard analog computer components in conjunction with a Kerr apparatus. The resulting displays give the entire rotational astroid and completely avoid wall switching and blocking phenomena. Examples are shown of applications of the astroid plotter with particular emphasis on obtaining the influence of bit geometry for all orientations of magnetization.