13 research outputs found
Magnetic ground state of the one-dimensional ferromagnetic chain compounds M(NCS)2(thiourea)2 (M=Ni,Co)
The magnetic properties of the two isostructural molecule-based magnetsâNi(NCS)2(thiourea)2, S = 1 [thiourea = SC(NH2 )2] and Co(NCS)2 (thiourea)2, S = 3/2âare characterized using several techniques in order to rationalize their relationship with structural parameters and to ascertain magnetic changes caused by substitution of the spin. Zero-field heat capacity and muon-spin relaxation measurements reveal low-temperature long-range ordering in both compounds, in addition to Ising-like (D < 0) single-ion anisotropy (DCo ⌠â100 K, DNi ⌠â10 K). Crystal and electronic structure, combined with dc-field magnetometry, affirm highly quasi-onedimensional behavior, with ferromagnetic intrachain exchange interactions JCo â +4 K and JNi ⌠+100 K and weak antiferromagnetic interchain exchange, on the order of J ⌠â0.1 K. Electron charge- and spin-density mapping reveals through-space exchange as a mechanism to explain the large discrepancy in J-values despite, from a structural perspective, the highly similar exchange pathways in both materials. Both species can be compared to the similar compounds MCl2(thiourea)4, M = Ni(II) (DTN) and Co(II) (DTC), where DTN is known to harbor two magnetic-field-induced quantum critical points. Direct comparison of DTN and DTC with the compounds studied here shows that substituting the halide Clâ ion for the NCSâ ion results in a dramatic change in both the structural and magnetic properties