Interaction of domain walls and magnetic nanoparticles in giant magnetoresistive nanostrips for biological applications

Head-to-head domain walls (DW) are formed and detected in U-shaped spin valve nanostrips by a Bitter Method on scanning electron microscope. We find that optimization of the washing technique is critical to proper deposition of magnetic nanoparticles (MNPs). The DW position is monitored electrically with giant magnetoresistance (GMR) similar to a potentiometer. DWs are repeatedly pinned and depinned from a site near the device center using a stage with two axis field. We first confirm the distribution of depinning events from a random sample of devices and obtain a standard deviation of 2.2 Oe. We then obtain an experimental signal of 8 Oe shift in depinning field from just 7 MNPs of 35 nm diameter.