With new technologies being developed, everything is becoming smaller. Firearms are being reduced in size to the point where the metal detectors of today cannot detect them properly. The use of giant magnetoresistant islands in metal detectors will increase sensitivity to metals and result in increased efficiency in detectors.

Giant magnetoresistant behavior (GMR) is exhibited when magnetic islands are present in a conductive matrix. To achieve this, a layer of copper ~20-50Å (angstroms) thick is deposited on a silicon wafer using an ion beam assisted deposition (IBAD) system. Above the copper, a layer of cobalt ~50-100Å is deposited, once again, using the IBAD system. Next, a blend of polymers (polystyrene and polymethyl-methacrylate) is spun cast on the sample. The sample is then annealed at 170°C for four days. Annealing the sample allows the polymers to separate and form islands on top of the metal substrate. The polymeric islands serve as a template for the magnetoresistant islands. The sample is then placed in an ion mill, where the polymer and parts of the metal substrate are sputtered off with Argon ions. What is left on the silicon wafer is a pattern of Co islands, ~50-100Å thick. At this height GMR behavior is the greatest. Finally, another layer of copper approximately the same thickness as the first is deposited.

To test for GMR, a four-point probe is used. The four-point probe detects changes in resistivity when constant voltage and current is applied. If the islands exhibit GMR behavior, a drastic change in resistivity is observed. Changes in resistivity are due to the spin of the electrons in the layers of Cu and Co. When a magnetic field passes through a GMR device, the spins of the electrons in the device align. Alignment of the spins is what causes the change in resistivity. This change in resistivity is seen when a metal object passes through a metal detector with GMR islands.

This equation (see pdf version below) is used to measure change in resistance. Samples with GMR behavior usually have a high ratio . . .however, it is more important to see a drastic change in resistance at low applied fields for practical application in metal detectors. It is expected that the samples created will exhibit GMR behavior because they have all of the characteristics of a GMR material.

Funding for this study was provided by Simons Grant 265210.

FOR PDF version of abstract with equations, click here: