Regensburg 2016 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe
TT: Fachverband Tiefe Temperaturen
TT 3: Correlated Electrons: Frustrated Magnets - Pyrochlore Systems and Iridates
TT 3.2: Vortrag
Montag, 7. März 2016, 09:45–10:00, H20
Unusual spin frozen state in a frustrated pyrochlore system NaCaCo2F7 as observed by NMR — •R. Sarkar1, J. W. Krizan2, F. Brückner1, R. J. Cava2, and H.-H Klauss1 — 1IFP, TU Dresden, D-01069 Dresden, Germany — 2Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
We present 23Na -and 19F NMR results on the magnetically frustrated pyrochlore NaCaCo2F7 with a frustration index of f = θCW/Tf ∼56. Recent neutron scattering experiments proposed XY like antiferromagnetic spin clusters at low energies in NaCaCo2F7. 23Na NMR -spectra reveal the presence of two magnetically non equivalent Na sites in conjunction with the local Co2+ spin structure. Below 3.6 K both the 23Na -and 19F spectra broaden due to the formation of static spin correlations. A huge reduction of the 19F -and 23Na NMR signal intensity hints at a quasi-static field distribution in NaCaCo2F7 in this regime. The 19F spin-lattice relaxation rate 19(1/T1) exhibits a peak at around 2.9 K, at the same temperature range where ac and dc susceptibility data show a broad maximum. The character of the spin fluctuation appears to be isotropic. The overall temperature dependence of 19(1/T1) can be described by the BPP theory considering a fluctuating hyperfine field with an autocorrelation function. The correlation time of the autocorrelation function exhibits an activation behavior further indicating the spin-frozen state. While the present NMR studies suggest the spin frozen state at low temperatures, µSR investigations however reveal the presence of so called persistent spin dynamics down to 20 mK implying an exotic ground state in NaCaCo2F7.