## Abstract

We present new and refined data for the magnetic field (H) and temperature (T) dependence of the proton spin-lattice relaxation rate (1/T_{1}) in antiferromagnetic molecular rings as well as a new explicit scaling formula that accurately reproduces our data. The key ingredients of our formulation are (1) a reduced relaxation rate, R(H,T) = (1/T_{1})/(Tχ(T)), given by R(H,T)=Aω_{c}(T)/(ω_{c}
^{2}(T) + ω_{N}
^{2}), where χ=(∂M/∂H)_{T} is the differential susceptibility, A is a fitting constant, and ω_{N} is the proton Larmor frequency, and (2) a temperature-dependent correlation frequency ω_{c}(T) which at low T is given by ω_{c}(T) ∝T^{α}, that we identify as a lifetime broadening of the energy levels of the exchange-coupled paramagnetic spins due to spin-acoustic phonon coupling. The main consequences are (1) R(H,T) has a local maximum for fixed H and variable T that is proportional to 1/H; the maximum occurs at the temperature T_{0}(H) for which ω_{c}(T) = ω_{N}; (2) for low T a scaling formula applies, R(H,T)/R(H,T_{0}(H))=2t^{α}/(1+t ^{2α}), where t≡T/T_{0}(H). Both results are confirmed by our experimental data for the choice α=3.5±0.5.

Original language | English |
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Article number | 134434 |

Journal | Physical Review B - Condensed Matter and Materials Physics |

Volume | 70 |

Issue number | 13 |

DOIs | |

Publication status | Published - Oct 2004 |

## ASJC Scopus subject areas

- Condensed Matter Physics