Regensburg 2002 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

TT: Tiefe Temperaturen

TT 5: Niedrigdimensionale Systeme, Magnetotransport I

TT 5.2: Vortrag

Montag, 11. März 2002, 15:00–15:15, H20

Synthesis, Structure and Magnetic Properties of Pb₂VO(PO₄)₂: The second example for a frustrated S=1/2 square lattice Antiferromagnet — •E. E. Kaul¹, C. Geibel¹, A. V. Mironov², R. V. Shpanchenko², and E. V. Antipov² — ¹Max-Planck Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden, Germany — ²Moscow State University, Dep. of Chemistry, Moscow 119899, Russia

Among low dimensional spin systems, frustrated S=1/2 square lattice systems have attracted strong theoretical interest, since an interesting phase diagram and unusual ground states are expected depending on the strength of the diagonal frustrating exchange J₂. However, experimental studies were very limited since the only compound where such spin system is realized (Li₂VOA⁺⁴O₄ (A=Si, Ge)) was discovered only 2 years ago. We have discovered a new compound, Pb₂VO(PO₄)₂ where the structural data as well as susceptibility and specific heat measurements suggest that such a frustrated S=1/2 lattice is also realized. Pb₂VO(PO₄)₂ has a structure formed by layers composed by S=1/2 V⁺⁴ in pyramidal coordination connected by PO₄ tetrahedra similar to that found in Li₂VOA⁺⁴O₄ (A=Si, Ge) but modulated along b. These layers are well separated by layers of Pb atoms and isolated PO₄ tetrahedra. Magnetic Susceptibility measurements shows a clear maximum at T_Max ≈ 8.7 K with a decrease towards lower temperatures. At T ≈ 3.6K we observe a very weak magnetic transition which becomes very pronounced and shifts to higher temperatures with applied magnetic field. This suggest that Pb₂VO(PO₄)₂ is very close to a quantum critical point.