Spin gap in a quasi-one-dimensional S= (1) /(2) antiferromagnet: Cu{sub 2}(1,4-diazacycloheptane){sub 2}Cl{sub 4}

Journal Article · Wed Apr 01 04:00:00 EST 1998 · Physical Review, B: Condensed Matter

DOI:https://doi.org/10.1103/PhysRevB.57.7846· OSTI ID:627552

Hammar, P R; Reich, D H; Broholm, C ^[1]; Trouw, F ^[2]

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1. Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland21218 (United States)
2. IPNS, Argonne National Laboratories, Argonne, Illinois60439 (United States)

Cu{sub 2}(1,4-diazacycloheptane){sub 2}Cl{sub 4} contains double chains of spin- (1) /(2) Cu{sup 2+} ions. We report ac susceptibility, specific heat, and inelastic neutron-scattering measurements on this material. The magnetic susceptibility {chi}(T) shows a rounded maximum at T=8 K indicative of a low-dimensional antiferromagnet with no zero-field magnetic phase transition. We compare the {chi}(T) data with exact diagonalization results for various one-dimensional spin Hamiltonians and find excellent agreement for a spin ladder with intrarung coupling J{sub 1}=1.143(3) meV and two mutually frustrating interrung interactions J{sub 2}=0.21(3) meV and J{sub 3}=0.09(5) meV. The specific heat in zero field is exponentially activated with an activation energy {Delta}=0.87(1) meV. A spin gap is also found through inelastic neutron scattering on powder samples that identify a band of magnetic excitations for 0.8{lt}{h_bar}{omega}{lt}1.5 meV. Using sum rules we derive an expression for the dynamic spin-correlation function associated with noninteracting propagating triplets in a spin ladder. The Van Hove singularities of such a model are not observed in our scattering data, indicating that magnetic excitations in Cu{sub 2}(1,4-diazacycloheptane){sub 2}Cl{sub 4} are more complicated. For magnetic fields above H{sub c1}{approx_equal}7.2 T specific-heat data versus temperature show anomalies indicating a phase transition to an ordered state below T=1 K. {copyright} {ital 1998} {ital The American Physical Society}

• OSTI ID: 627552
• Journal Information: Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 13 Vol. 57; ISSN PRBMDO; ISSN 0163-1829
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANTIFERROMAGNETIC MATERIALS
CORRELATIONS
ENERGY GAP
EXCITATION
MAGNETIC SUSCEPTIBILITY
NEUTRON DIFFRACTION
ORGANIC COMPOUNDS
SPECIFIC HEAT
SPIN