A MOSSBAUER STUDY OF TEMPERATURE-DRIVEN SPIN REORIENTATIONS IN DY1-XHOXFEO3

Single crystals of the mixed rare-earth orthoferrite Dy1-xHoxFeO3 (x = 0.25, 0.5, and 0.75) have been studied by Mossbauer spectroscopy in t he 1.3-298 K temperature range. Several temperature-induced Fe3+ spin reorientation transitions have been observed. On cooling, a locally di scontinuous reorientation from the a to the b orthorhombic axis took p lace near 40 K followed by a continuous reorientation from the b to th e c axis. The onset temperature of the latter transition depends linea rly on Ho concentration x. An x-T phase diagram of Dy1-xHoxFeO3 is pro posed which extrapolates well to the results of previous studies of pu re HoFeO3 and pure DyFeO3. The continuous Fe3+ spin reorientation in t he be plane showed the hyperfine interactions of the Fe-57 nuclei to s plit into two branches. This branching is associated with different Fe unit cell positions. The temperature variation of the difference in m agnetic hyperfine fields agrees well with a previous calculation of a similar effect in NMR. We also observed a new, very sharp Fe3+ spin re orientation from the c to the b orthorhombic axis upon cooling a Dy(0. 75)Ho(0.25)PeO(3) single-crystal absorber between 3 K and 2.3 K. We su ggest that this transition is driven by ordering of the rare-earth spi ns and a microscopic mechanism is proposed.