Magnetic structures of nearly isostructural <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Tb</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>RuO</mml:mi><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Nd</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>RuO</mml:mi><mml:mn>7</mml:mn></mml:msub></mml:mrow></mml:math> : Appearance of a partially …

We report on the magnetic structures of ${\mathrm{Tb}}_{3}{\mathrm{RuO}}_{7}$ and ${\mathrm{Nd}}_{3}{\mathrm{RuO}}_{7}$ determined from powder neutron-diffraction experiments. In ${\mathrm{Tb}}_{3}{\mathrm{RuO}}_{7}$, alternating-bond spin-$\frac{3}{2}$ Ru1-Ru2 chains are formed. The Ru1 Ru2 moments ordered disordered (paramagnetic), respectively, below 15 K. This result indicates appearance a partially (PD) state, although two Ru sites very similar to each other. ${\mathrm{Nd}}_{3}{\mathrm{RuO}}_{7}$, ions form independent uniform chains. Both 17.5 Probably, main source PD state in is frustration exchange interactions. internal field generated by Tb at different that sites. speculate (nonuniform) enhances difference properties between moments. also entropy changes ${\mathrm{Gd}}_{3}{\mathrm{RuO}}_{7}$.