Abstract:
We have studied the processes of atomic and magnetic ordering in the hydrides of the metastable Laves phases $R$Mn$_2$D$_{3-\delta}$ ($R$ = Y, Tb, and Dy; $\delta\le$ 0.14) in the temperature range from 2 to 300 K and the pressure range from 0 to 6 GPa by X-ray and neutron diffraction methods. We found that a hydrogen superstructure with symmetry reduction to P6$_3$/m is formed in the hydrides $R$Mn$_2$D$_{3-\delta}$ near room temperature. A number of unusual magnetic phenomena that have never been observed in the hexagonal Laves hydrides $R$Mn$_2$D$_x$ was found, namely, the coexistence of ferrimagnetic and antiferromagnetic orderings in $R$Mn$_2$D$_{3-\delta}$ ($R$ = Tb, Dy) and pressure-induced transition from the ferrimagnetic to antiferromagnetic state in TbMn$_2$D$_{2.86}$. It has been suggested that the topology of the crystal lattice plays an important role in the formation of the magnetic properties of the hexagonal hydrides $R$Mn$_2$D$_{3-\delta}$.
Keywords:rare earth intermetallics, hydrides, magnetostructural transition, neutron diffraction, high pressures.
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