Resistance measurement of GMR heads as a magnetic performance indicator

The resistance of spin valve GMR heads as a function of current was studied, which was correlated with the magnetic performances of heads. The "assist" current gives larger DC resistance of MR elements than the "against" current. The physical origin of this resistance difference is the spin-valve (SV) effect due to current direction. The resistance difference is defined as Delta MRR- = MRR- - MRR+ where MRR- and MMR+ are MR resistances measured with negative (assist) and positive (against) current directions, respectively. This resistance difference has a good correlation with MR amplitude of SV. As an application, it is shown that the resistance difference well reflects the MR amplitude of electrostatic discharge (ESD) stressed GMR heads. In this study, a simple and new method was suggested to evaluate MR amplitudes of SV by measuring the resistance difference of GMR heads with a digital multimeter (DMM). The method reported here can be generally used to screen ESD-damaged heads and to evaluate the magnetic performance during various stages of the GMR head manufacturing processes and failure analysis. This method does not require any external magnetic field. Therefore, this can also be used for accelerated life test of GMR heads in an oven, where the external magnetic field can not be easily applied.