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TT: Tiefe Temperaturen
TT 18: Niederdimensionale Systeme, Magnetotransport, Quantenhalleffekt I
TT 18.6: Talk
Wednesday, March 28, 2001, 17:15–17:30, A
Magnetic-Field Induced Gap and Staggered Susceptibility in the S = 1/2 Chain PMCu(NO3)2(H2O)2 (PM = pyrimidine) — •Ralf Feyerherm1, Michael Meissner1, and Takayuki Ishida2 — 1Hahn-Meitner-Institut, Glienicker Str. 100, 14109 Berlin — 2Dept. of Applied Physics and Chemistry, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
Single crystal magnetic susceptibility and specific heat studies of the one-dimensional copper complex PMCu(NO3)2(H2O)2(PM = pyrimidine) show that it behaves like a uniform S = 1/2 antiferromagnetic Heisenberg chain (J/kB = 36 K). Specific heat measurements in applied magnetic field, however, reveal the formation of a field induced spin excitation gap, whose magnitude depends on the magnitude and direction of the field. This behaviour is inconsistent with the ideal S = 1/2 Heisenberg chain. In the low-temperature region, a contribution to the susceptibility approximately proportional to 1/T is observed that strongly varies with varying direction of the magnetic field. The field induced gap and the 1/T contribution are largest for the same field direction. Previous observations of a field induced gap in the related compound copper benzoate have been explained by the alternating g tensor and alternating Dzyaloshinkii-Moriya interaction, producing an effective staggered magnetic field at the Cu ions. We apply this model to PMCu(NO3)2(H2O)2 and obtain a consistent quantitative explanation of the low-temperature susceptibility, the field induced gap and their dependence on the magnetic field direction [R. Feyerherm et al., J. Phys.: Condens. Matter 12 (2000) 8495].