Near-ideal molecule-based Haldane spin chain

Abstract

The molecular coordination complex NiI2(3,5-lut)4 [where (3,5-lut) = (3,5-lutidine) = (C7H9N)] has been synthesized and characterized by several techniques including synchrotron X-ray diffraction, ESR, SQUID magnetometry, pulsed-field magnetization, inelastic neutron scattering and muon spin relaxation. Templated by the configuration of 3,5-lut ligands the molecules pack in-registry with the Ni-I· · · I-Ni chains aligned along the c-axis. This arrangement leads to through-space I· · · I magnetic coupling which is directly measured for the first time in this work. The net result is a near-ideal realization of the S = 1 Haldane chain with J = 17.5 K and energy gaps of ∆ = 5.3 K ∆ ⊥ = 7.7 K, split by the easy-axis single-ion anisotropy D = −1.2 K. The ratio D/J = −0.07 affords one of the most isotropic Haldane systems yet discovered, while the ratio ∆0/J = 0.40(1) (where ∆0 is the average gap size) is close to its ideal theoretical value, suggesting a very high degree of magnetic isolation of the spin chains in this material. The Haldane gap is closed by orientation-dependent critical fields µ0H c = 5.3 T and µ0H ⊥ c = 4.3 T, which are readily accessible experimentally and permit investigations across the entirety of the Haldane phase, with the fully polarized state occurring at µ0H s = 46.0 T and µ0H ⊥ s = 50.7 T. The results are explicable within the so-called fermion model, in contrast to other reported easy-axis Haldane systems. Zero-field magnetic order is absent down to 20 mK and emergent end-chain effects are observed in the gapped state, as evidenced by detailed low-temperature measurements. arXiv:1909.07900v1 [cond-mat.str-el]

Magneto-structural Correlations in Ni2+–Halide···Halide–Ni2+ Chains

“…NiI 2 (3,5-lut) 4 has been previously characterized by Williams et al 19 and exhibits easy-axis single-ion anisotropy with D = −1.2(3) K, which was extracted from inelastic neutron scattering measurements. Pulsed-field magnetization shows a very high saturation field relative to the other compounds reported here, indicating strong antiferromagnetic interactions of J = 17.5(1) K along the Ni–I···I–Ni chains.…”

“…The complete phase diagram for these systems displays Ising and XY -ordered states along with two gapped phases: the Haldane and quantum paramagnetic states (see Figure ). It has already been shown that NiI 2 (3,5-lut) 4 is a highly isotropic [ D / J = −0.07(1)] example of a Haldane chain . In addition, because it displays no magnetic order even when the Haldane gap has been closed by the application of an applied magnetic field, the value of J ⊥ in this material is believed to be extremely small.…”

“…Compounds for which J ⊥ values are not quantitatively established are represented by arrows along the x -axis. From the results in ref ( 19 ), it is known that the J ⊥ / J ratio for NiI 2 (3,5-lut) 4 is extremely small. We expect it will be the same for the isostructural NiBr 2 (3,5-lut) 4 .…”

SquidLab—A user-friendly program for background subtraction and fitting of magnetization data

“…The dipole fits performed by SquidLab are shown as black lines through the background subtracted data. The example samples shown are (a) an S = 1 1D molecule-based magnet [11], with low density of magnetic ions, dispersed in the pressure medium of a piston-cylinder pressure cell (Quantum Design and partners), (b) diamagnetic sample Pd 3 P 2 S 8 mounted on a standard quartz sample holder and (c) a molecular framework antiferromagnet pressed pellet within a pressure cell (Camcool Research Ltd) [12]. In all these cases there is no evident dipole in the raw data at the sample position and hence fitting and extraction of the magnetic moment is not possible.…”

Long-Range Order and Quantum Criticality in Antiferromagnetic Chains with Long-Range Staggered Interactions

“…The remarkable difference between one-dimensional (1D) AFM systems of integer and halfinteger spins opens a highly successful avenue in understanding the low-dimensional strongly correlated electronic materials. The isotropic Heisenberg AFM model has been unexpectedly coined in a number of nearly ideal quasi-one-dimensional materials such as Cu(C 4 H 4 N 2 )(NO 3 ) 2 [17], Sr 2 Cu(PO 4 ) 2 [18], KCuF 3 [19], CuSO 4 ⋅5D 2 O [20], and spin-1 chain materials like SrNi 2 V 2 O 8 [21,22], Ni(C 2 H 8 N 2 ) 2 NO 2 (ClO 4 ) [23,24] and * wlyou@nuaa.edu.cn NiI 2 (C 7 H 9 N) 4 [25]. There have also been attempts to realize spontaneous symmetry breaking and develop true AFM order in spin-1/2 Heisenberg chains.…”