Larson and Pirich showed that the MnBi fiber spacing in the Mn–Bi system is finer when the alloy is solidified in space or in the presence of a magnetic field. In completion of a program aimed at explaining these results, the influence of electric current pulses on the MnBi fiber spacing is determined. Small, frequent electric current pulses cause fiber spacing to increase. The fiber spacing is roughly proportional to the length of the current pulse and its amplitude. An additional piece of information is the recent results by Smith, showing no influence of low gravity on the MnBi fiber spacing. Consequently now the Larson‐Pirich results are believed to be caused by a fluctuating freezing rate on earth, resulting from time‐dependent buoyancy‐driven convection. The fiber spacing adjusts more readily to a sudden decrease in freezing rate than it does to a sudden increase in freezing rate. That is, the MnBi fibers are terminated more readily than they branch. If the reverse is true, then a fluctuating freezing rate would cause a decrease in fiber spacing rather than an increase.