Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 20: Correlated Electrons - Poster Session

TT 20.31: Poster

Mittwoch, 28. März 2007, 14:00–17:45, Poster A

In₂VO₅ - a new low dimensional S = 1/2 system probed by magnetic resonance — •M. Yehia¹, E. Vavilova¹, T. Taetz², A. Möller², V. Kataev¹, B. Büchner¹, N. Hollmann³, and J.A. Mydosh³ — ¹Institute for Solid State and Materials Research IFW Dresden, D-01171 Dresden, Germany — ²Institut für Anorganische Chemie, Universität zu Köln, 50939 Köln, Germany — ³II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany

In₂VO₅ contains paramagnetic V⁴⁺ (3d¹, S =1/2) ions. The structural feature is a double chain of VO₆-polyhedra along the b-axis. X-ray diffraction reveals a change of the lattice contraction from isotropic at high T to anisotropic below 150 K. In the spin sector this leads to a change in the spin topology from coupled S = 1/2 chains to coupled S = 1/2 triangles along the b-axis. ESR and ⁵¹V NMR data give evidence that the structural changes have a strong impact on the magnetic properties. The static susceptibility suggests a transition from ferromagnetic exchange above a characteristic temperature T^* ∼ 120 K to antiferromagnetic (AF) exchange at T < T^*. ESR and NMR reveal a slowing of the d-electron spin dynamics as a consequence of enhanced AF correlations at T < T^* and an AF ordering at ∼20 K. Remarkably, a well defined ESR signal from V⁴⁺ ions can only be observed below T^*, strongly suggesting the localization of the d-states. Indeed, the resistivity data, ρ(T), show a dramatic increase of ρ and a transition to an insulating behaviour at T < T^*. We discuss these experimental observations in terms of a significant interplay between structure, magnetism and charge mobility in this novel material.