%0 Journal Article %1 PhysRevB.103.014428 %A Opherden, D %A Bärtl, F %A Yamamoto, Sh %A Zhang, Z T %A Luther, S %A Molatta, S %A Wosnitza, J %A Baenitz, M %A Heinmaa, I %A Stern, R %A Landee, C P %A Kühne, H %D 2021 %I American Physical Society %J Phys. Rev. B %K b %N 1 %P 014428 %R 10.1103/PhysRevB.103.014428 %T Freezing of molecular rotation in a paramagnetic crystal studied by $^31$P NMR %U https://journals.aps.org/prb/pdf/10.1103/PhysRevB.103.014428 %V 103 %X We present a detailed 31P nuclear magnetic resonance (NMR) study of the molecular rotation in the compound Cu(pz)2(2−HOpy)2(PF6)2, where pz=C4H4N2 and 2−HOpy=C5H4NHO. Here, a freezing of the PF6 rotation modes is revealed by several steplike increases of the temperature-dependent second spectral moment, with accompanying broad peaks of the longitudinal and transverse nuclear spin-relaxation rates. An analysis based on the Bloembergen-Purcell-Pound (BPP) theory quantifies the related activation energies as Ea/kB=250 and 1400 K. Further, the anisotropy of the second spectral moment of the 31P absorption line was calculated for the rigid lattice, as well as in the presence of several sets of PF6 reorientation modes, and is in excellent agreement with the experimental data. Whereas the anisotropy of the frequency shift and enhancement of nuclear spin-relaxation rates is driven by the molecular rotation with respect to the dipole fields stemming from the Cu ions, the second spectral moment is determined by the intramolecular interaction of nuclear 19F and 31P moments in the presence of the distinct rotation modes.

@article{PhysRevB.103.014428, abstract = {We present a detailed 31P nuclear magnetic resonance (NMR) study of the molecular rotation in the compound [Cu(pz)2(2−HOpy)2](PF6)2, where pz=C4H4N2 and 2−HOpy=C5H4NHO. Here, a freezing of the PF6 rotation modes is revealed by several steplike increases of the temperature-dependent second spectral moment, with accompanying broad peaks of the longitudinal and transverse nuclear spin-relaxation rates. An analysis based on the Bloembergen-Purcell-Pound (BPP) theory quantifies the related activation energies as Ea/kB=250 and 1400 K. Further, the anisotropy of the second spectral moment of the 31P absorption line was calculated for the rigid lattice, as well as in the presence of several sets of PF6 reorientation modes, and is in excellent agreement with the experimental data. Whereas the anisotropy of the frequency shift and enhancement of nuclear spin-relaxation rates is driven by the molecular rotation with respect to the dipole fields stemming from the Cu ions, the second spectral moment is determined by the intramolecular interaction of nuclear 19F and 31P moments in the presence of the distinct rotation modes.}, added-at = {2021-10-14T16:42:09.000+0200}, author = {Opherden, D and Bärtl, F and Yamamoto, Sh and Zhang, Z T and Luther, S and Molatta, S and Wosnitza, J and Baenitz, M and Heinmaa, I and Stern, R and Landee, C P and Kühne, H}, biburl = {https://www.bibsonomy.org/bibtex/2183360222b3fb3d4a0b640dd4e84d26e/ctqmat}, day = 19, description = {Freezing of molecular rotation in a paramagnetic crystal studied by 31P NMR}, doi = {10.1103/PhysRevB.103.014428}, interhash = {035aef3b7b33868773638d0fc7df22bd}, intrahash = {183360222b3fb3d4a0b640dd4e84d26e}, journal = {Phys. Rev. B}, keywords = {b}, month = {01}, number = 1, numpages = {8}, pages = 014428, publisher = {American Physical Society}, timestamp = {2023-10-19T10:33:33.000+0200}, title = {Freezing of molecular rotation in a paramagnetic crystal studied by $^{\mathbf{31}}$P NMR}, url = {https://journals.aps.org/prb/pdf/10.1103/PhysRevB.103.014428}, volume = 103, year = 2021 }