Brenda A. Everitt

Size dependence of switching thresholds for pseudo spin valve MRAM cells

For magnetoresistive random access memory (MRAM) to be a successful new memory technology, very dense cells with high output are necessary. As bit sizes shrink, it becomes advantageous to employ memory modes in which the uniaxial anisotropy lies along the length of the bit. For bits smaller than approximately 0.2 μm in width, curling across the bit becomes small, and the magnetization may be treated as a uniform single domain. We have modeled “pseudo spin valve” MRAM cells in the single-domain approximation. Calculations in this size regime for asymmetric giant magnetoresistive (GMR) sandwich material reveal that switching thresholds are sensitive to bit size. Submicron cells 0.4 μm×2.2 μm in size have been patterned from asymmetric GMR sandwich material and switching thresholds compare favorably with the single-domain model. These “pseudo spin valve” memory cells are very promising for nonvolatile, high speed, high-density memories.

Exchange coupling of radio frequency sputtered NiMn/NiFe and NiFe/NiMn bilayers

Exchange coupling of radio frequency sputtered NiMn/NiFe (NiMn on top) and NiFe/NiMn (NiMn at bottom) bilayers have been investigated. It was found that the exchange coupling field, Hex, is not only directly related with the annealing temperature and time, but also is greatly influenced by the thin film deposition conditions. It was demonstrated that successful antiferromagnetic-ferromagnetic bilayer preparation should avoid interfacial contamination, which could destroy the spin coupling at the interface. The NiFe/NiMn bilayers show a high exchange coupling field [307 Oe for NiFe(200 A)/NiMn(500 A)] bilayer with a high blocking temperature around 430 °C. Most important is that the coupling field was able to sustain its strength up to almost 270 °C before starting to decrease. X-ray diffraction reveals that the diffraction intensity of NiMn in as-deposited bilayers does not seem important to achieve a high exchange coupling field. Furthermore, the NiMn thickness dependence of the magnetic properties of Ni...

Enhanced giant magnetoresistance sandwich film

Devices have been patterned from enhanced sandwich material as well as more conventional giant magnetoresistance (GMR) sandwich material. The enhanced GMR sandwich consists of essentially adding a Cu spacer and a synthetic antiferromagnet layer to either side of a conventional sandwich stack. While devices patterned from simple sandwich material are always high resistance in the zero field bias state and decrease in resistance in an applied field, similar devices fabricated from enhanced sandwich material exhibit more complex characteristics. Depending upon the bias current density, the zero field biased state may be either low or high resistance for this structure. This effect could be useful for applications such as current or magnetic field sensing.