Colossal magnetostriction and negative thermal expansion in the frustrated antiferromagnet ZnCr2Se4

TL;DR

This study reveals that ZnCr2Se4 exhibits colossal magnetostriction and negative thermal expansion due to spin-driven lattice frustration, with quantum critical behavior induced by magnetic fields.

Contribution

It provides detailed experimental evidence of spin-driven structural instability and colossal magnetostriction in a frustrated antiferromagnet, highlighting the role of competing exchange interactions.

Findings

Negative thermal expansion below 75 K

Colossal magnetostriction of 0.5x10^{-3}

Suppression of antiferromagnetic order by magnetic field

Abstract

A detailed investigation of ZnCr2Se4 is presented which is dominated by strong ferromagnetic exchange but orders antiferromagnetically at T_N = 21 K. Specific heat C and thermal expansion Delta L/L exhibit sharp first-order anomalies at the antiferromagnetic transition. T_N 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 T_N 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 T_N explained in terms of competing ferromagnetic and antiferromagnetic exchange interactions yielding strong bond frustration.