Magnetic ground state of the one-dimensional ferromagnetic chain compounds (NCS)2(thiourea)2 ( =Ni,Co)
S. P. M. Curley, R. Scatena, R. C. Williams, P. A. Goddard, P. Macchi, T. J. Hicken, T. Lancaster, F. Xiao, S. J. Blundell, V. Zapf, J. C. Eckert*, E. H. Krenkel, J. A. Villa, M. L. Rhodehouse, and J. L. Manson
Physical Review Materials 5, 034401 (2021)
Abstract
The magnetic properties of the two isostructural molecule-based magnets—Ni(NCS)2(thiourea)2, =1 [thiourea=SC(NH2)2] and Co(NCS)2(thiourea)2, =3/2—are 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 ( <0) single-ion anisotropy ( Co∼−100 K, Ni∼−10 K). Crystal and electronic structure, combined with dc-field magnetometry, affirm highly quasi-one-dimensional behavior, with ferromagnetic intrachain exchange interactions Co≈+4 K and Ni∼+100 K and weak antiferromagnetic interchain exchange, on the order of ′∼−0.1 K. Electron charge- and spin-density mapping reveals through-space exchange as a mechanism to explain the large discrepancy in -values despite, from a structural perspective, the highly similar exchange pathways in both materials. Both species can be compared to the similar compounds Cl2(thiourea)4, = 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 Cl− ion for the NCS− ion results in a dramatic change in both the structural and magnetic properties.