  HoFe1-xMnxO3 (0 < x < 1) single crystals have been grown by the optical
floating zone technique. A structural transition from the orthorhombic to
hexagonal modification has been established in the crystals in the
concentration range of 0.7-0.8, which has been confirmed by the X-ray
diffraction data. For a series of the rhombic crystals, the room-temperature
Mossbauer study and magnetic measurements in the temperature range of 4.2-1000
K have been carried out. It has been observed that, with an increase in the
manganese content in the samples, the temperature of the spin-reorientation
transition increases significantly: from 60 K in the HoFeO3 compound to room
temperature in HoFe0.6Mn0.4O3. The magnetic measurements have shown that, upon
substitution of manganese for iron, the magnetic orientational type transition
changes from a second-order transition (AxFyGz -> CxGyFz) to first-order one
(AxFyGz -> GxCyAz) with a weak ferromagnetic moment only in the b direction
(for Pnma notation). The growth of the spin-reorientation transition
temperature has been attributed to the change in the value of the indirect
exchange in the iron subsystem under the action of manganese, which has been
found when studying the Mossbauer effect in the HoFe1-xMnxO3 (x < 0.4)
compound.
