NMR investigation of Gd(hfac)3NITEt fully frustrated helimagnet

The family of the quasi-1D molecular magnetic chains Gd(hfac)3NITR (where hfac is hexafluoro-acetylacetonate and NITR is 2-R-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-l-oxyl 3-oxyde) have assumed a great importance in the study of molecular magnets in the last 10 years. These chains develop along b crystallographic axis and consist in a regular pattern of Gd(hfac)3 moieties (S_Gd=7/2) alternated to nitronyl-nitroxide organic radicals NITR (R = iPr, Et, Ph, Me) (srad=1/2). In these derivatives the shortest interchain distance is about 10.5Å and, as a consequence, the ratio between interchain and intrachain exchange interactions is Jinter/Jintra1.9K while just below the transition temperature T(c)^3D=1.9K becomes suddenly much larger (>1 MHz), due to the insurgence of a local field Hloc at protons sites, generated by the ordered arrangement of the electronic spins