Abstract
The hyperfine interactions of the iron nuclei in the orthoferrites were studied between 85 and 770°K using the Mössbauer effect. The temperature dependence of the sublattice magnetization is compared with various statistical-mechanical theories. It obeys approximately a power law in the temperature range , and spin-wave theory and Callen decoupling at low temperature in the range . From , it is found that the canting angle in these weak ferromagnets is temperature-independent. The exchange integral calculated from the Oguchi spin-wave theory agrees with that calculated from Rushbrook and Wood's high-temperature series expansion and the Green's-function theories, while that calculated from the molecular field and Kubo's spin-wave theories is considerably lower. The quadrupole coupling constant is in good agreement with values calculated by point-charge lattice sums. The specific heat obtained from the temperature shift at high temperature agrees with the Dulong-Petit law. The value of the isomer shift is equal to that expected for a trivalent iron ion.
- Received 31 October 1966
DOI:https://doi.org/10.1103/PhysRev.156.562
©1967 American Physical Society