Cross-tie/Bloch line detection

Abstract

Electronic detection of cross-tie/Bloch line pairs is essential for the use of these pairs as data bits in a serial access memory. The physical size of the cross-ties and Bloch lines is small and their associated magnetic flux is weak. Results obtained to data indicate that the detection of cross-tie/Bloch line pairs based on magnetoresistive principles is the most feasible and practical for memory array applications. Three detector designs, fabrication techniques and experimental results are presented. The detectors consist of two gold electrodes 1500 Å thick, separated by a small gap. Under the detector is an isotropic or anisotropic NiFe film serration 350 Å thick. The gap in the detector is placed on a cross-tie or Bloch line position and is shaped so as to maximize the resistance change in the magnetoresistive film for a ’’zero’’ and ’’one’’ state. The relationships between sensing current and magnetization distributions are described with the aid of Lorentz electron micrographs. Normal signal levels for the most promising design are in the range of 15–20 μV/mA. Sensing currents of 5–6 mA are used which produce safe current densities, thus typically yielding 100 μV signals.