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]
The [Zn
1–
x
Ni
x
(HF
2
)(pyz)
2
]SbF
6
(
x
= 0.2; pyz = pyrazine)
solid solution exhibits a zero-field
splitting (
D
) that is 22% larger [
D
= 16.2(2) K (11.3(2) cm
–1
)] than that observed
in the
x
= 1 material [
D
= 13.3(1)
K (9.2(1) cm
–1
)]. The substantial change in
D
is accomplished by an anisotropic lattice expansion in
the MN
4
(M = Zn or Ni) plane, wherein the increased concentration
of isotropic Zn(II) ions induces a nonlinear variation in M-F and
M-N bond lengths. In this, we exploit the relative donor atom hardness,
where M-F and M-N form strong ionic and weak coordinate covalent bonds,
respectively, the latter being more sensitive to substitution of Ni
by the slightly larger Zn(II) ion. In this way, we are able to tune
the single-ion anisotropy of a magnetic lattice site by Zn-substitution
on nearby sites. This effect has possible applications in the field
of single-ion magnets and the design of other molecule-based magnetic
systems.
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