Magnetic structures and magnetic phase transitions in rare-earth $R$Mn$_{2}$Si$_{2}$ intermetallic compounds ($R$ = Sm, Tb)

The magnetic structures that form in La$_{1-x}R_{x}$Mn$_{2}$Si$_{2}$ ($R$ = Sm, Tb) layered compounds with various concentrations $x$ have been determined by magnetic neutron diffraction and magnetic measurements, and the magnetic phase diagrams have been built. It is shown that the formation of the magnetic structures is dependent not only on exchange interactions, but also on the type of the magnetic anisotropy of a rare-earth atom. It is found that, in La$_{1-x}R_{x}$Mn$_{2}$Si$_{2}$ compounds with 0.2 $< x <$ 0.5, the competition of the Tb–Mn and Mn–Mn interlayer exchange interactions and the existence of a strong uniaxial magnetic anisotropy in the Mn and Tb sublattices leads to the frustrated magnetic state and prevents the formation of the long-range magnetic order in the Tb sublattice.