Investigation of switching characteristics of nanomagnets via magnetic force microscopy

Magnetic quantum cellular automata (MQCA) have been proposed as an alternate computing architecture. Single domain magnetic particles represent "1" or "0"; their stray field interaction controls the propagation and manipulation of information. An inherent requirement for an MQCA system is to know the conditions under which nanomagnets switch between the purely "up" (1) and the purely "down" (0) state, and to control this reproducibly.As a first step to study this, arrays of two types of permalloy particles were designed, simulated, fabricated and imaged, and their switching distributions ascertained. Individual particles were "peanut"-shaped, to investigate the effect of a shape anisotropy for an elliptical particle. Particles had long axes of 750 nm and 250 nm, but had identical aspect ratios.Particles were simulated with a public domain software package, Object Oriented Micromagnetic Framework (OOMMF), fabricated by electron beam lithography with standard lift-off techniques in the fabrication facility in Sherbrooke, Canada, and imaged in vacuum using a custom built magnetic force microscope in constant height mode with an in plane, in-situ magnetic field. Ensemble hysteresis loops were obtained as was the average switching fields for both arrays.The 750 nm particles were found experimentally to have a two-step switching process. The first switch occurred at 60 +/- 16 Oe and the second at 130 +/- 56 Oe. These results were nominally better than those obtained in a previous study on similarly sized ellipses.Simulations on the 250 nm particles predicted that particles of that size would have the single domain configuration as their virgin state, and would have a one-step switching process. The switching field of a typical particle was calculated to be 550 +/- 30 Oe. This was confirmed experimentally, where the switching field distribution had its peak at 490 +/- 40 Oe. Thus, theory and experiment are in agreement, within error