Antiferromagnetic exchange in two-leg spin-1/2 ladders
- Ames Laboratory-U.S. DOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)
Extraction of antiferromagnetic (AF) exchange constants {ital J} and {ital J}` in two-leg spin-1/2 nearest-neighbor (NN) Heisenberg ladders from experimental magnetic spin susceptibility {chi}({ital T}) data is studied, where {ital J}{prime} is the NN exchange constant in the rungs and {ital J} is that in the legs. Two low-{ital T} ({ital T}{lt}{ital J}/{ital k}{sub {ital B}}) approximations of Troyer, Tsunetsugu, and W{umlt u}rtz for {chi}({ital T}) of the isolated spin-1/2 two-leg ladder with {ital J}{prime}/{ital J}=1 are shown to be accurate to {approximately}10{percent} when extrapolated to {ital T{approx}J`/k{sub B}}. The variations in the magnetic excitation dispersion relation parameters which enter the low-{ital T} expression of Troyer {ital et al}. for {chi}({ital T}) for {ital J`/J}{lt}1 are inferred from previous theoretical results. Next, the values of the maxima in {chi}({ital T})={chi}{sup max} from many numerical calculations in the literature for various nonfrustrated spin-1/2 NN Heisenberg antiferromagnets are considered. The values of the product {chi}{sup max}{ital z}{sub eff} are found to depend systematically and almost uniqely on an effective magnetic coordination number {ital z}{sub eff}, defined in the text, but are nearly independent of the dimensionality of the spin lattice and of the magnitude of any gap in the magnetic excitation spectrum. This observation allows accurate bounds on the exchange coupling constants in arbitrary quasi-low-dimensional spin-1/2 antiferromagnets to be inferred from experimental {chi}{sup max} values. Finally, a mean-field-type expression for {chi}({ital T}) for arbitrary quasi-low-dimensional spin-1/2 Heisenberg antiferromagnets is derived, using the above {chi}{sup max} phenomenology as input, which allows the influence of intersystem coupling on {chi}({ital T}) to be evaluated. These results, and the {chi}({ital T}) calculations of Barnes and Riera [Phys. Rev.
- Research Organization:
- Ames National Laboratory
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 392130
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 54, Issue 18; Other Information: PBD: Nov 1996
- Country of Publication:
- United States
- Language:
- English
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