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MA: Magnetismus
MA 27: Spin-Dynamics, Magnetization Reversal II
MA 27.5: Talk
Thursday, March 30, 2006, 11:15–11:30, HSZ 403
SPIN STATE BLOCKADE AT METAL-INSULATOR PHASE TRANSITION IN LAYERED COBALTITES RBaCo2O5.5 RAMAN STUDIES — •Yurii Pashkevich1, Vladimir Gnezdilov2, Peter Lemmens3, Claudia Ambrosch-Draxl4, Karina Lamonova1, Alexander Gusev1, Kwang-Yong Choi5, Sergei Barilo6, Sergei Shiryaev6, and Georgii Bychkov6 — 1A. A. Galkin Donetsk Phystech NASU, 83114 Donetsk, Ukraine — 2B. I. Verkin Institut for Low Temperature Physics NASU, 61164 Kharkov, Ukraine — 3Institut für Physik d. Kondensierten Materie, D-38106 Braunschweig, Germany — 4Institut für Theoretische Physik, Universität Graz, A-8010 Graz, Austria — 5Institute for Material Research, Tohoku University, Katahira 2-1-1 Sendai 980-8577, Japan — 6Institute of Physics of Solids & Semiconductors, ASB, 220072 Minsk, Belarus
Using Raman spectroscopy and ab-initio lattice dynamic calculations we uncover the structure of spin states below TMI=350 K in single crystalline RBaCo2O5.5 (R=Gd, Eu). In GdBaCo2O5.5 we observe the G-type of high spin (HS) and intermediate spin (IS) state order of Co-octahedral sites which placed in ac-plane, while pyramidal sites remains in IS states all the way up to 400 K. We show that this type of spin state order strongly suppresses carrier’s motion and lead to the anisotropy of resistivity. Below 200 K we observe the gap opening between HS and IS states in XZ-spectra (this gap equals to 55 cm−1 at 5 K).