|
Magnetic structure of the yttrium orthoferrite YFeO3 (space group Pbmn – D162h can be treated as consisting of the two sublattices antiferromagnetically ordered (TN = 640 K) along the a-axis and slightly canted towards the c-axis. Investigating low-frequency AFMR mode (300 GHz at zero magnetic field) at temperatures 4.2 – 70 K and magnetic field up to 14 T we observed five additional well resolved and rather intensive impurity modes [1]. Since no magnetic impurities were measured in the sample by x-ray-fluorescent analysis with the accuracy 10-5, these "impurity" modes were assigned to the electron transitions between the levels of a 6S5/2 multiplet of the Fe+3 ions which occupy the 4c-positions of the Y+3 ions instead of their regular 4b-positions. Because of these positions symmetry the 6S5/2 multiplet is split into six non-equidistant levels both by an exchange interaction with the host matrix and by a crystal field. The impurity ions are magnetized by the effective field approximatly 9 T along the c-axis opposite to the weak ferromagnetic moment. Magnetic field applied alond the antiferromagnetic axis (a-axis) induces spin reorientation (SR) from the a- to the c-axis with partial softening of the AFMR mode [2] that results in crossing of the AFMR and impurity modes during SR at H < Htr (Htr - field of the SR completion, see Fig.). "Impurity" spins coupled with the host matrix also rotate from the c- to the a-axis, so that at the fields H > Htr they are directed strictly opposite the applied field. Thus, after SR complition the relative arrangement of the sublattices magnetisation, impurity spins and magnetic field is quite the same as in the case H ∥ c-axis [1] and in addition, we can investigate the crossing of the ascending AFMR mode with the five descanding "impurity" modes.
|
