Journal article · Preprint article
Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4
Paul Scherrer Institute1
Augsburg University2
Nano-Microstructures in Materials, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark3
Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark4
Risø National Laboratory for Sustainable Energy, Technical University of Denmark5
Academy of Sciences of Moldova6
Leibniz Institute for Solid State and Materials Research Dresden7
Laboratrio Nacional de Luz Síncrotron8
Helmholtz Centre Berlin for Materials and Energy9
Institut Laue-Langevin10
...and 0 moreWe study the evidence for spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single-crystal neutron scattering in zero and applied magnetic fields. The magnetically ordered phase appearing below T-N = 8 K remains nonconventional down to 1.5 K. The magnetic Bragg peaks at the q = 0 positions are broad and their line shapes have strong Lorentzian contributions.
Additionally, the peaks are connected by weak diffuse streaks oriented along the <111 > directions. The observed short-range magnetic correlations are explained within the spiral spin-liquid model. The specific shape of the energy landscape of the system, with an extremely flat energy minimum around q = 0 and many low-lying excited spiral states with q = <111 >, results in thermal population of this manifold at finite temperatures.
The agreement between the experimental results and the spiral spin-liquid model is only qualitative, indicating that microstructure effects might be important to achieve quantitative agreement. Application of a magnetic field significantly perturbs the spiral spin-liquid correlations. The magnetic peaks remain broad but acquire more Gaussian line shapes and increase in intensity.
The 1.5 K static magnetic moment increases from 1.58 mu(B)/Co at zero field to 2.08 mu(B)/Co at 10 T. The magnetic excitations appear rather conventional at zero field. Analysis using classical spin-wave theory yields values of the nearest- and next-nearest-neighbor exchange parameters J(1) = 0.92(1) meV and J(2) = 0.101(2) meV and an additional anisotropy term D = -0.0089(2) meV for CoAl2O4.
In the presence of a magnetic field, the spin excitations broaden considerably and become nearly featureless at the zone center.
Language: | English |
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Year: | 2011 |
ISSN: | 1550235x , 10980121 , 10953795 and 01631829 |
Types: | Journal article and Preprint article |
DOI: | 10.1103/PhysRevB.84.094403 |
ORCIDs: | Christensen, Niels Bech |