Theoretical estimates for proton-NMR spin–lattice relaxation rates of heterometallic spin rings

Heterometallic molecular chromium wheels are fascinating new magnetic materials. We reexamine the available experimental susceptibility data on MCr 7 wheels in terms of a simple isotropic Heisenberg Hamiltonian for M=Fe, Ni, Cu, and Zn and find in that FeCr 7 needs to be described with an iron–chrom...

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Veröffentlicht in:Journal of magnetism and magnetic materials 2006-07, Vol.302 (1), p.206-210
Hauptverfasser: Allalen, Mohammed, Schnack, Jürgen
Format: Artikel
Sprache:eng
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Zusammenfassung:Heterometallic molecular chromium wheels are fascinating new magnetic materials. We reexamine the available experimental susceptibility data on MCr 7 wheels in terms of a simple isotropic Heisenberg Hamiltonian for M=Fe, Ni, Cu, and Zn and find in that FeCr 7 needs to be described with an iron–chromium exchange that is different from all other cases. In a second step we model the behavior of the proton spin lattice relaxation rate as a function of applied magnetic field for low temperatures as it is measured in nuclear magnetic resonance (NMR) experiments. It appears that CuCr 7 and NiCr 7 show an unexpectedly reduced relaxation rate at certain level crossings.
ISSN:0304-8853
DOI:10.1016/j.jmmm.2005.09.006