We
report the results of 57Fe Mössbauer study
of iron-based compounds BaRFeO4 (R = Y, Dy), which undergo two magnetic phase transitions
at T
N1 ≈ 47 K (Y, Dy) and T
N2 ≈ 35 K (Y), 23 K (Dy). The first transition
(T
N1) is related to a phase transformation
from the paramagnetic state into a spin-density wave (SDW), and the
second one (T
N2) is associated with a
phase transition to the cycloidal spin structure (CSS). Mössbauer
measurements at various temperatures were performed to clarify the
magnetic behavior of these phases. In the intermediate-temperature
range T
N2 < T < T
N1, our investigations indicate an incommensurate
SDW phase with the inclusion of many high-order harmonics. For both
the ferrites, the modulated incommensurate cycloid with the iron moments
within the bc plane was supported at a low-temperature
range of T < T
N2.
In contrast to BaDyFeO4, where the magnetic structure changes
abruptly at ∼T
N2, a region of coexistence
between the SDW and CSS phases (ΔT ≈
13 K) was observed for BaYFeO4. Magnetic measurements confirmed
the phase transitions detected by Mössbauer spectroscopy and
revealed an additional transition at T
N3 ≈ 9 K in BaDyFeO4, which is not manifested in
the Mössbauer spectra below this transition point.