Switching anomaly and magnetization vortices of 200 Å thick NiFeCo elements in one-micron patterned arrays

One-micron patterned arrays of 200 Angstrom thick NiFeCo elements show an interesting switching anomaly. Depending on the starting held of a hysteresis loop, H-m, magnetization reversal can occur at one or two well-defined fields. The fraction of the elements that switch at one or the other field depends on H-m,. The number of elements that switch at one field starting from a given H-m depends on past history. Magnetic force microscopy shows that trapped vortices from a previous reversal are found to be responsible for this switching anomaly. Increasing H-m lowers the probability of vortex formation. (C) 1999 Elsevier Science B.V. All rights reserved.