Muoniated radical formation and spin dynamics in molecular magnetic materials with oxalate ligands

The crystal structure of Na 2T 2(ox) 2(H 2O) 2 with T = Ni ( II ) , Co ( II ) , Fe ( II ) , and Mn(II) consists of isostructural compounds with an anionic transition metal oxalate network with a 2-leg ladder topology. We performed zero external field μ SR , longitudinal-field quenching (LFQ) and avoided level-crossing (ALC) measurements on the Co-compound of this series. The measurements show that a significant fraction of the implanted muons forms a muoniated radical state by muonium addition to the resonant π electron system of the ( COO ) 2 2 - group. The LFQ measurements reveal electronic spin fluctuation rates of several GHz. For reference, ALC measurements on the nonmagnetic compounds Li 2(ox) 2 and Na 2(ox) 2 were carried out and the muon hyperfine coupling constant were deduced to 115 and 150 MHz, respectively.