No abstract

No abstract

Micro-Hall sensors have been fabricated, and various numbers of micron-size magnetic beads have been placed within the sensor area. The Hall resistances measured at room temperature are found to be proportional to the number of the beads, and are in good agreement with the numerically simulated results presented in this study. Our sensors are designed to measure the number of beads between zero and full-scale signals for a given number range of interest. The effects of miniaturizing the beads and sensors to nanoscale are also discussed.

We have investigated the effects of texture and interfacial roughness on the exchange anisotropy in NiFe/Cu/NiFe/FeMn spin valves with different buffer layers (no buffer, Cu, or FeMn) on Si(100) or Si(111) substrates by magnetron sputtering. The crystalline structure, surface topology, and exchange anisotropy field (Hex) were characterized. The exchange anisotropy was established all in (111), (200), and (220) textured samples and there was no systematic relationship between the type of texture and Hex. However, it was found that Hex increased as the surface roughness decreased. The results lead us to believe that interfacial roughness rather than crystallographic texture controls the development of the exchange anisotropy.

An abrupt change of conductance at a threshold magnetic field was observed in a device consisting of a nonmagnetic narrow-gap semiconductor. The conductance varies more than 25 times as the magnetic field increases. The threshold magnetic field can be tuned using a bias voltage from zero to several hundred Gauss. This large magnetoconductance effect is caused by the magnetic field-dependent impact ionization process. A theoretical model is proposed, and calculations based on this model simulate the experimental results closely. This device may be a good candidate for an electrical switching device controlled by a magnetic field.