We have studied magnetic tunnel junction (MTJ) thin-film stacks using the First Order Reversal Curve (FORC) method. These have very sharp structures in the FORC distribution, unlike most particulate systems or patterned films. These structures are hard to study using conventional FORC analysis programs that require smoothing, because this washes out the structure. We have used a new analysis program (FORC+) that is designed to distinguish fine-scale structure from noise without the use of smoothing, to identify these structures and gain information about the switching mechanism of the stack.

This research utilizes particle swarm optimization (PSO) to minimize the total active power losses in an IEEE 6bus transmission system. The complexity of the problem lies in integrating Newton-Raphson load flow algorithm, which is used in computing power losses, with PSO algorithm, which is used to minimize these losses. The considered PSO control variables are: the reactive power output of generators, the tap ratios of transformers, and the reactive power output of shunt compensators. PSO was chosen as optimization method due to its popularity as a successful algorithm in solving non-smooth global optimization problems. The proposed PSO algorithm gave very satisfactory simulation results. Power losses were reduced by 13.9% for an initial set of PSO parameters. These parameters were thereafter varied in order to improve PSO performance by further minimizing the power losses. Effectively, we were able to obtain a set of parameters that resulted in a 19.31% reduction in power losses. These successful simulation results confirm the effectiveness of PSO in minimizing distribution networks power losses.

Recent research on CoPd alloys with perpendicular magnetic anisotropy (PMA) has suggested that they might be useful as the pinning layer in CoFeB/MgO-based perpendicular magnetic tunnel junctions (pMTJ's) for various spintronic applications such as spin-torque transfer random access memory (STT-RAM). We have previously studied the effect of seed layer and composition on the structure (by XRD, SEM, AFM and TEM) and performance (coercivity) of these CoPd films. These films do not switch coherently, so the coercivity is determined by the details of the switching mechanism, which was not studied in our previous paper. In the present paper, we show that information can be obtained about the switching mechanism from magnetic force microscopy (MFM) together with first order reversal curves (FORC), despite the fact that MFM can only be used at zero field. We find that these films switch by a mechanism of domain nucleation and dendritic growth into a labyrinthine structure, after which the unreversed domains gradually shrink to small dots and then disappear.

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To raise the areal density of magnetic recording to ∼1 Tbit/in2, there has been much recent work on the use of FePt granular films, because their high perpendicular anisotropy allows small grains to be stable. However, their coercivity may be higher than available write-head fields. One approach to reduce the coercivity is to heat the grain (heat assisted magnetic recording). Another strategy is to add a soft capping layer to help nucleate switching via exchange coupling with the hard FePt grains. We have simulated a model of such a capped medium and have studied the effect of the strength of the interface exchange and thickness of hard layer and soft layer on the overall coercivity. Although the magnetization variation within such boundary layers may be complex, the net effect of the boundary can often be modeled as an infinitely thin interface characterized by an interface exchange energy density—we show how to do this consistently in a micromagnetic simulation. Although the switching behavior in the presence of exchange, magnetostatic, and external fields is quite complex, we show that by adding these fields one at a time, the main features of the M-H loop can be understood. In particular, we find that even without hard-soft interface exchange, magnetostatic coupling eliminates the zero-field kink in the loop, so that the absence of the kink does not (as has sometimes been assumed) imply exchange coupling. The computations have been done with a public-domain micromagnetics simulator that has been adapted to easily simulate arrays of grains.