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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Numerical investigation of spin excitations in a doped spin chain

We study the doping evolution of spin excitations in a one-dimensional (1D) Hubbard model and its downfolded spin Hamiltonians, by using exact diagonalization combined with cluster perturbation theory. In all models we observe hardening (softening) of spin excitations upon electron (hole) doping, which are reminiscent of recent experiments on two-dimensional (2D) cuprate materials. We also find that the three-site and even higher-order terms are crucial for the low-energy effective spin models to reproduce the magnetic spectra of doped Hubbard systems at a quantitative level. To interpret the numerical results, we further employ a strong coupling slave-boson mean-field theory. The mean-field theory provides an intuitive understanding of the overall compact support of dynamic spin structure factors, including the shift of zero-energy modes and change of spin excitation bandwidth with doping. Our results can serve as predictive benchmarks for future inelastic x-ray or neutron scattering experiments on doped 1D antiferromagnetic Mott insulators.

Pärschke, Ekaterina M.↗
DOE OSTI2021

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 magnets— Ni ( NCS ) 2 ( thiourea ) 2 , S = 1 [ thiourea = SC ( NH 2 ) 2 ] and Co ( NCS ) 2 ( thiourea ) 2 , S = 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 ( D < 0 ) single-ion anisotropy ( D Co ~ - 100 K, D Ni ~ - 10 K). Crystal and electronic structure, combined with dc-field magnetometry, affirm highly quasi-one-dimensional behavior, with ferromagnetic intrachain exchange interactions J Co ≈ + 4 K and J Ni ~ + 100 K and weak antiferromagnetic interchain exchange, on the order of J ' ~ - 0.1 K. Furthermore, 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 M Cl 2 ( 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 Cl - ion for the NCS - ion results in a dramatic change in both the structural and magnetic properties.

36 MATERIALS SCIENCE↗