Scaling behavior of the proton spin-lattice relaxation rate in antiferromagnetic molecular rings

S. H. Baek, M. Luban, A. Lascialfari, E. Micotti, Y. Furukawa, F. Borsa, J. van Slageren, and A. Cornia
Phys. Rev. B 70, 134434 – Published 29 October 2004

Abstract

We present new and refined data for the magnetic field (H) and temperature (T) dependence of the proton spin-lattice relaxation rate (1T1) 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)=(1T1)(Tχ(T)), given by R(H,T)=Aωc(T)(ωc2(T)+ωN2), where χ=(MH)T is the differential susceptibility, A is a fitting constant, and ωN is the proton Larmor frequency, and (2) a temperature-dependent correlation frequency ωc(T) which at low T is given by ωc(T)Tα, 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 1H; the maximum occurs at the temperature T0(H) for which ωc(T)=ωN; (2) for low T a scaling formula applies, R(H,T)R(H,T0(H))=2tα(1+t2α), where tTT0(H). Both results are confirmed by our experimental data for the choice α=3.5±0.5.

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  • Received 18 May 2004

DOI:https://doi.org/10.1103/PhysRevB.70.134434

©2004 American Physical Society

Authors & Affiliations

S. H. Baek1,*, M. Luban1, A. Lascialfari2, E. Micotti2, Y. Furukawa3, F. Borsa1,2, J. van Slageren4, and A. Cornia5

  • 1Department of Physics and Astronomy, Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
  • 2Dipartimento di Fisica “A. Volta” e Unita INFM di Pavia, Via Bassi 6, 27100 Pavia, Italy
  • 3Division of Physics, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
  • 4INSTM and Dipartimento di Chimica, Università di Firenze, I-50019 Sesto Fiorentino(FI), Italy
  • 5Dipartimento di Chimica-Centro SCS, Università di Modena e Reggio Emilia, UdR INSTM, I-41100, Modena, Italy

  • *Electronic address: baek@ameslab.gov

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Issue

Vol. 70, Iss. 13 — 1 October 2004

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