Large magnetostriction and negative thermal expansion in the frustrated antiferromagnet ZnCr2Se4

A detailed investigation of ZnCr2Se4 is presented which is dominated by strong ferromagnetic exchange but orders antiferromagnetically at T-N = 21 K. Specific heat and thermal expansion exhibit sharp first-order anomalies at the antiferromagnetic transition. T-N is shifted to lower temperatures by external magnetic fields and finally is fully suppressed by a field of 65 kOe. The relative length change Delta L/L(T) is unusually large and exhibits negative thermal expansion alpha below 75 K down to T-N indicating strong frustration of the lattice. Magnetostriction Delta L/L(H) reveals large values comparable to giant magnetostrictive materials. These results point to a spin-driven origin of the structural instability at T-N explained in terms of competing ferromagnetic and antiferromagnetic exchange interactions.