Dresden 2006 – scientific programme

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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 RBaCo₂O_5.5 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 T_MI=350 K in single crystalline RBaCo₂O_5.5 (R=Gd, Eu). In GdBaCo₂O_5.5 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).