Low-temperature deviations from Bloch’s law in BaFe12O19 hexaferrite.

The NMR method is used to study the temperature variations of local fields on 57Fe nuclei in the octahedral positions 12k, 4f2, and 2a of the iron ions in the ferrite BaFe12O19. The possibility of applying Bloch’s spin-wave theory to describe the temperature variations of the local fields on the iron nuclei is examined. Deviations from Bloch’s 3/2 power law are found in the temperature range 4.2–77 K. These deviations cannot be described on the basis of the behavioral characteristics due to the presence of an energy gap in the acoustic magnon spectrum. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]