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High-order coupled cluster method study of frustrated and unfrustrated quantum magnets in external magnetic fields

Farnell, Damian J. J., Zinke, R., Schulenburg, J. and Richter, J. 2009. High-order coupled cluster method study of frustrated and unfrustrated quantum magnets in external magnetic fields. Journal of Physics: Condensed Matter 21 (40) , 406002. 10.1088/0953-8984/21/40/406002

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We apply the coupled cluster method (CCM) in order to study the ground-state properties of the (unfrustrated) square-lattice and (frustrated) triangular-lattice spin-half Heisenberg antiferromagnets in the presence of external magnetic fields. Here we determine and solve the basic CCM equations by using the localised approximation scheme commonly referred to as the `LSUBm ' approximation scheme and we carry out high-order calculations by using intensive computational methods. We calculate the ground-state energy, the uniform susceptibility, the total (lattice) magnetisation and the local (sublattice) magnetisations as a function of the magnetic field strength. Our results for the lattice magnetisation of the square-lattice case compare well to those results of QMC for all values of the applied external magnetic field. We find a value for magnetic susceptibility of χ=0.070 for the square-lattice antiferromagnet, which is also in agreement with the results of other approximate methods (e.g., χ=0.0669 via QMC). Our estimate for the range of the extent of the (M/M s = )1 3 magnetisation plateau for the triangular-lattice antiferromagnet is 1.37<λ<2.15 , which is in good agreement with results of spin-wave theory (1.248<λ<2.145 ) and exact diagonalisations (1.38<λ<2.16 ). The CCM value for the in-plane magnetic susceptibility per site is χ=0.065 , which is below the result of the spin-wave theory (evaluated to order 1/S) of χ SWT =0.0794.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Dentistry
Subjects: Q Science > QC Physics
Publisher: IOP Publishing
ISSN: 0953-8984
Last Modified: 04 Jun 2017 06:23

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