Wall Stability of Cylindrical (Bubble) Domains in Thin Films and Platelets

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Abstract
The stability in an applied magnetic field of a domain of reversed magnetization in an otherwise uniformly magnetized thin‐film medium, has been investigated experimentally and theoretically. From a free energy point of view, a field applied antiparallel to the magnetization of the reversed domain tends to affect the size of the domain based on energy minimization. Assuming a cylindrical domain, we have: (1) calculated the total energy due to the domain wall, the magnetostatic field, and the applied field; (2) compared the inward force on the domain wall derived from this total energy with a coercivity or retarding force to establish a threshold applied field for domain motion; and (3) compared theoretical predictions with experimental results in both MnBi films and an orthoferrite platelet. Comparisons were based on values of saturation magnetization and domain‐wall energy density which are believed typical or have been reported elsewhere. Agreement of the data with calculation is considered satisfactory for both media. The requirement of accurately measuring MnBi spots of the order of 1 μ in size was met using an automatic Faraday modulation polarimeter. A detailed description of this novel instrument is included.

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