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Colossal magnetostriction and negative thermal expansion in the frustrated antiferromagnet ZnCr2Se4

J. Hemberger, H. -A. Krug von Nidda, V. Tsurkan, A. Loidl

cond-mat.mtrl-sciarXiv:cond-mat/0607811

Abstract

A detailed investigation of ZnCr2Se4 is presented which is dominated by strong ferromagnetic exchange but orders antiferromagnetically at TN = 21 K. Specific heat C and thermal expansion Delta L/L exhibit sharp first-order anomalies at the antiferromagnetic transition. TN is strongly reduced and shifted to lower temperatures by external magnetic fields and finally is fully suppressed suggesting a field induced quantum critical behavior close to 60 kOe. Delta L/L(T) is unusually large and exhibits negative thermal expansion below 75 K down to TN indicating strong frustration of the lattice. Magnetostriction Delta L/L(H) reveals colossal values (0.5x10-3) comparable to giant magnetostriction materials. Electron-spin resonance, however, shows negligible spin-orbital coupling excluding orbitally induced Jahn-Teller distortions. The obtained results point to a spin-driven origin of the structural instability at TN explained in terms of competing ferromagnetic and antiferromagnetic exchange interactions yielding strong bond frustration.

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