# Structure and magnetism in the bond-frustrated spinel $$ZnCr_2Se_4$$

Zajdel, P., Li, W.-Y., van Beek, W., Lappas, A., Ziolkowska, A., Jaskiewicz, S., Stock, C., Green, M.A. (2017) Structure and magnetism in the bond-frustrated spinel $$ZnCr_2Se_4$$. Physical Review B, 95 (13). Article Number 134401. ISSN 2469-9950. (doi:10.1103/PhysRevB.95.134401) (KAR id:61902)

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The crystal and magnetic structures of stoichiometric $$ZnCr_2Se_4$$ have been investigated using synchrotron x-ray and neutron powder diffraction, muon spin relaxation ($$μSR$$), and inelastic neutron scattering. Synchrotron x-ray diffraction shows a spin-lattice distortion from the cubic $$Fd\bar3m$$ spinel to a tetragonal $$I4_1/amd$$ lattice below $$T_N = 21 K$$, where powder neutron diffraction confirms the formation of a helical magnetic structure with magnetic moment of $$3.04(3) μ_B$$ at 1.5 K, close to that expected for high-spin $$Cr^{3+}$$. $$μSR$$ measurements show prominent local spin correlations that are established at temperatures considerably higher (<100 K) than the onset of long-range magnetic order. The stretched exponential nature of the relaxation in the local spin-correlation regime suggests a wide distribution of depolarizing fields. Below $$T_N$$, unusually fast ($$>100 μs^{-1}$$) muon relaxation rates are suggestive of rapid site hopping of the muons in static field. Inelastic neutron scattering measurements show a gapless mode at an incommensurate propagation vector of k = [000.4648(2)] in the low-temperature
magnetic ordered phase that extends to 0.8 meV. The dispersion is modeled by a two-parameter Hamiltonian, containing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions with a $$J_{nnn}/J_{nn} = -0.337$$.