Probing magnetic order and disorder in the one-dimensional molecular spin chains CuF2(pyz) and [Ln(hfac)3(boaDTDA)]n (Ln=Sm, La) using implanted muons

We present the results of muon-spin relaxation ($mu^{+}$SR) measurements on antiferromagnetic and ferromagnetic spin chains. In antiferromagnetic CuF$_{2}$(pyz) we identify a transition to long range magnetic order taking place at $T_{mathrm{N}} = 0.6(1)$ K, allowing us to estimate a ratio with the intrachain exchange of $T_{mathrm{N}}/|J| approx 0.1$ and the ratio of interchain to intrachain exchange coupling as $|J/J| approx 0.05$. The ferromagnetic chain [Sm(hfac)$_{3}$(boaDTDA)]$_{n}$ undergoes an ordering transition at $T_{mathrm{c}}=2.8(1)$ K, seen via a broad freezing of dynamic fluctuations on the muon (microsecond) timescale and implying $T_{mathrm{c}}/|J| approx 0.6$. The ordered radical moment continues to fluctuate on this timescale down to 0.3 K, while the Sm moments remain disordered. In contrast, the radical spins in [La(hfac)$_{3}$(boaDTDA)]$_{n}$ remain magnetically disordered down to $T=0.1$ K suggesting $T_{mathrm{c}}/|J| < 0.17$.