Rapid detection of defects in LPE bubble crystals

Magnetic defects disturbing the reliable operation of bubble domain devices were detected by scanning an arrayed stripe domain band which was generated by a pair of permanent magnets. A condition suitable for the defect detection was examined, especially as for the magnetic field gradient applied. Comparative values of the coercive fields of the defects were deduced by the measurement of the field difference along the full length of the stretched stripe domains pinned by the defects. An instrumental technique has been devised for automatic imperfection mapping. Electrical signals from a scanning line on a TV monitor are used for the detection. Imperfections are plotted on an X-Y recorder by amplifying the signals. This sensitive method easily located imperfections found with difficulty by other methods and has been successfully used to evaluate the LPE garnet films for device applications.