Irreversible remagnetisation processes in nano- and microstructured Nd-Fe-B alloys at low temperatures

The low temperature magnetisation jumps have been observed and studied in nano- and microstructured alloys based on the Nd₂Fe₁₄B phase. “Barkhausen-like” jumps can be explained in terms of the two-stage trigger/propagation model. Magnetisation jumps cause the internal parts of the sample to heat up to a critical temperature. This is a temperature at which no magnetisation jumps are observed on the remagnetisation curve. Magnetisation jumps can be activated in some samples by their local heating with electric current pulses. When magnetic alloy powder was placed in a nonmagnetic matrix, increasing the average distance between ferromagnetic particles, the number of magnetisation jumps decreased. The remagnetisation mechanism in alloys changes from a two-stage trigger/propagation process, which occurs in the nanostructured samples, to a thermal activation process, which occurs in the microstructured samples. The increase in grain size leads to a decrease in the critical temperature value at which magnetisation jumps can be observed.