Berlin 2012 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 45: Correlated Electrons: Poster Session

TT 45.60: Poster

Donnerstag, 29. März 2012, 15:00–19:00, Poster B

NMR on the quasi two-dimensional antiferromagnet Ba(Ni_1−xMg_x)₂V₂O₈ — •Dirk Waibel¹, Thomas Wolf², Hilbert v. Löhneysen^1,2, and Bernd Pilawa¹ — ¹Karlsruher Institut für Technologie, Physikalisches Institut, 76131 Karlsruhe — ²Karlsruher Institut für Technologie, Institut für Festkörperphysik, 76021 Karlsruhe

Magnetic-field dependent NMR measurements in the quasi two-dimensional (2D) antiferromagnet (AF) Ba(Ni_1−xMg_x)₂V₂O₈ have been performed for B⊥c and B∥c at 2 K and 79 MHz. The spin echo signal of the ⁵¹V nuclei in the undoped sample consists of one distinct peak for B∥c which is split into three lines for B⊥c. The signals of the ⁵¹V nuclei significantly broaden upon doping. Futhermore, the ⁵¹V nuclear spin-lattice relaxation rate T₁⁻¹ has been measured over a temperature range from 6 K to 300 K at 7 T and 79 MHz revealing a strong increase of the T₁⁻¹ rate at T_N = 47.4 K. This divergent behavior has been analyzed for B⊥c and B∥c in the context of the 2D topological Berezinskii-Kosterlitz-Thouless (BKT) phase transition. Also, the oscillatory decay of the spin echo due to the quadrupole interaction of the ⁵¹V (I=7/2) nuclei is clearly visible in the temperature range from 50 K to 300 K.