Regensburg 2004 – wissenschaftliches Programm
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MA: Magnetismus
MA 21: Bio- und molekularer Magnetismus
MA 21.3: Vortrag
Donnerstag, 11. März 2004, 10:45–11:00, H22
Observation of a transverse magnetization in the S=1/2 antiferromagnetic chain [PM·Cu(NO3)2·(H2O)2]n by 13C-NMR — •H.-H. Klauss1, A.U.B. Wolter1, P. Wzietek2, D. Jerome2, S. Süllow1, F.J. Litterst1, A. Honecker3, W. Brenig3, and R. Feyerherm4 — 1Institut für Metallphysik und Nukleare Festkörperphysik, TU Braunschweig — 2Laboratoire de Physique des Solides, Universite Paris-Sud, Orsay, France — 3Institut für Theoretische Physik, TU Braunschweig — 4Hahn-Meitner-Institut, Berlin
We present 13C-NMR studies of the static and dynamic magnetic properties of the S=1/2 antiferromagnetic chain [PM·Cu(NO3)2·(H2O)2 ]n. In this system the spin-orbit interaction gives rise to an anisotropic magnetic field induced spin excitation gap. The microscopic model used to describe the thermodynamic properties (M. Oshikawa and I. Affleck, PRL 79 2883) proposed the existence of a staggered magnetization component transverse to the applied field which cannot be measured macroscopically. We measured the local susceptibility via the NMR frequency shift at three different carbon sites in the pyrimidine molecule as a function of temperature and magnetic field orientation. The transverse staggered magnetization is identified as a low temperature deviation from the linear correlation between local and global susceptibility. The observed magnitude and temperature dependence are consistent with the theoretical model. The spin excitation gap is determined from the temperature dependence of the T1 relaxation rate. These measurements reveal additional excitations in the gap.