Exchange-coupled pair model for the random-exchange Heisenberg antiferromagnetic chain

Journal Article · Mon Oct 01 04:00:00 EDT 1979 · Phys. Rev., B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.20.2914· OSTI ID:5763374

Clark, W G; Tippie, L C

An approximate model for the s=1/2 one-dimensional Heisenberg antiferromagnet with random exchange is presented. A probability for exchange (J) of the form P (J) =const J/sup -alpha/, with the constant ..cap alpha.. in the range 0<..cap alpha..<1, is considered. The approximation is to decouple alternate spins, which leads to isolated exchange-coupled spin pairs having the same P (J). Explicit results for the magnetization (M), susceptibility (chi), entropy (S), and specific heat (C/sub H/) are given. Several limiting cases are worked out. The low-field (Zeeman energy very-much-less-thank/sub B/T) behavior is chi=const T/sup -alpha/, whereas at intermediate fields (Zeeman energy >>k/sub B/T), M=const H/sup 1-alpha/, and C/sub H/=const TH/sup -alpha/. These results are in agreement with the observed behavior of several tetracyanoquinodimethane (TCNQ) charge transfer salts with asymmetric donors, such as quinolinium- (TCNQ)/sub 2/. Comparison with other approximations shows this model to give results almost indistinguishable from the spinless fermion model of Bulaevskii et al. and the cluster model of Theodorou and Cohen. It is argued that the work of Alexander, Bernasconi, and Orbach shows that there is a relationship between the density of states and P (J) for the Heisenberg chain, and that they are not the same. This leads to a value of ..cap alpha.. for the thermodynamic properties which differs from that of P (J) for the fully coupled Heisenberg chain.

• Research Organization: Department of Physics, University of California at Los Angeles, Los Angeles, California 90024
• OSTI ID: 5763374
• Journal Information: Phys. Rev., B: Condens. Matter; (United States), Journal Name: Phys. Rev., B: Condens. Matter; (United States) Vol. 20:7; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ANTIFERROMAGNETISM
CRYSTAL MODELS
ENTROPY
HEISENBERG MODEL
HETEROCYCLIC COMPOUNDS
MAGNETIC PROPERTIES
MAGNETIC SUSCEPTIBILITY
MAGNETISM
MAGNETIZATION
MATHEMATICAL MODELS
NITRILES
ONE-DIMENSIONAL CALCULATIONS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PHYSICAL PROPERTIES
SPECIFIC HEAT
THERMODYNAMIC PROPERTIES
TTF-TCNQ