Regensburg 2010 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 27: CE: Poster Session

TT 27.67: Poster

Mittwoch, 24. März 2010, 14:00–18:00, Poster D1

ESR Studies of the Quantum Spin Dimer System Ba₃Cr₂O₈ — •D. Kamenskyi¹, J. Wosnitza¹, S.A. Zvyagin¹, J. Krzystek², A.A. Aczel³, H.A. Dabkowska³, and G.M. Luke³ — ¹Hochfeld-Magnetlabor Dresden, FZ Dresden - Rossendorf, Dresden, Germany — ²National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA — ³McMaster University, Hamilton, Ontario, Canada

Ba₃Cr₂O₈ is a system of three-dimensionally coupled dimers, exhibiting a field-induced phase transition from a quantum-disordered to a long-range antiferromagnetically ordered state at H_c1 = 12.5 T. We report tunable-frequency electron spin resonance (ESR) studies of Ba₃Cr₂O₈ single crystals performed in a frequency range between 50 and 700 GHz in fields up to 25 T (applied along the c axis). Two gaps in the magnetic excitation spectrum, Δ₁ = 564 GHz and Δ₂ = 400 GHz, were observed directly, confirming the spin-singlet ground state of Ba₃Cr₂O₈ below H_c1. The observation of singlet-triplet ESR transitions, which are normally forbidden in spin-1/2 dimer systems by selection rules, indicates the break-down of the axial symmetry in this compound. Details of the ESR excitation spectrum of Ba₃Cr₂O₈ across different regions of its phase diagram will be discussed.

This work was partly supported by the DFG and EuroMagNET (EU contract No. 228043).