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Title: Low temperature magnetic properties and spin dynamics in single crystals of Cr{sub 8}Zn antiferromagnetic molecular rings

A detailed experimental investigation of the effects giving rise to the magnetic energy level structure in the vicinity of the level crossing (LC) at low temperature is reported for the open antiferromagnetic molecular ring Cr{sub 8}Zn. The study is conducted by means of thermodynamic techniques (torque magnetometry, magnetization and specific heat measurements) and microscopic techniques (nuclear magnetic resonance line width, nuclear spin lattice, and spin-spin relaxation measurements). The experimental results are shown to be in excellent agreement with theoretical calculations based on a minimal spin model Hamiltonian, which includes a Dzyaloshinskii-Moriya interaction. The first ground state level crossing at μ{sub 0}H{sub c1} = 2.15 T is found to be an almost true LC while the second LC at μ{sub 0}H{sub c2} = 6.95 T has an anti-crossing gap of Δ{sub 12} = 0.19 K. In addition, both NMR and specific heat measurements show the presence of a level anti-crossing between excited states at μ{sub 0}H = 4.5 T as predicted by the theory. In all cases, the fit of the experimental data is improved by introducing a distribution of the isotropic exchange couplings (J), i.e., using a J strain model. The peaks at the first and second LCs in themore » nuclear spin-lattice relaxation rate are dominated by inelastic scattering and a value of Γ ∼ 10{sup 10} rad/s is inferred for the life time broadening of the excited state of the open ring, due to spin phonon interaction. A loss of NMR signal (wipe-out effect) is observed for the first time at LC and is explained by the enhancement of the spin-spin relaxation rate due to the inelastic scattering.« less
Authors:
 [1] ;  [2] ; ; ;  [3] ; ;  [4] ;  [5] ;  [4] ;  [2] ;  [6] ;  [4] ;  [2] ;  [7] ; ;  [8] ;  [9] ;
  1. Dipartimento di Fisica, Università degli Studi di Milano and INSTM, I-20133 Milano (Italy)
  2. (Italy)
  3. Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Parma, I-43124 Parma (Italy)
  4. CNR Institute Nanosciences S3, I- 41125 Modena (Italy)
  5. Dipartimento di Scienze Fisiche, Informatiche, Matematiche, Università di Modena e Reggio Emilia, I-41125 Modena (Italy)
  6. (Spain)
  7. Grenoble High Magnetic Field Laboratory, CNRS-LNCMI, 25, B.P. 166, 38042 Grenoble Cedex 9 (France)
  8. The Lewis Magnetism Laboratory, The University of Manchester, M13 9PL Manchester (United Kingdom)
  9. Dipartimento di Fisica, Università degli Studi di Pavia and INSTM, I-27100 Pavia (Italy)
Publication Date:
OSTI Identifier:
22493419
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 24; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANTIFERROMAGNETIC MATERIALS; ANTIFERROMAGNETISM; CHROMIUM BASE ALLOYS; EXCITED STATES; GROUND STATES; HAMILTONIANS; INELASTIC SCATTERING; LINE WIDTHS; MAGNETIC PROPERTIES; MAGNETIZATION; MONOCRYSTALS; NUCLEAR MAGNETIC RESONANCE; PHONONS; SPECIFIC HEAT; SPIN; SPIN-LATTICE RELAXATION; SPIN-SPIN RELAXATION; STRAINS; ZINC ALLOYS