Boundary for weak ferromagnetism in ${\mathrm{Sm}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Gd}}_{\mathit{x}}$${\mathrm{CuO}}_4$ solid solutions

Dc-magnetization and electron-spin-resonance measurements in the solid solutions ${\mathrm{Sm}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Gd}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ have shown weak ferromagnetism for 1<x≤2. Low-temperature values for the extrapolated spontaneous magnetization associated with a spin canting of the Cu moments, ${\mathit{M}}_{\mathrm{Cu}}$, and the internal magnetic field, ${\mathit{H}}_{\mathit{i}}^{\mathrm{Gd}}$, that polarizes the rare-earth ions have been determined. An exchange coupling constant ${\mathit{J}}_{\mathrm{Gd}\mathrm{-}\mathrm{Cu}}$=1.0(4) meV has been estimated from the ratio between these two parameters. Hysteresis loops show a small coercive field and differences in the remanent magnetization between field-cooled and zero-field-cooled samples. The possible relation of the boundary for weak ferromagnetism in the series of ${\mathit{R}}_2$ ${\mathrm{CuO}}_4$ cuprates with the existence of local static distortions of the lattice is discussed in terms of Dzyaloshinski-Moriya exchange interactions between the Cu ions.