Effect of pressure on 2-magnon Raman scattering in K2NiF4

Abstract We measured the effect of pressure ( P ⩽ 10 GPa) on 2-magnon excitations ( T = 10 K) and on lattice parameters ( T = 300 K) of K 2 NiF 4 by Raman spectroscopy and X-ray diffraction respectively. The results allow us to determine the dependence of the superexchange interaction J on the transition metal to anion distance d . We find that J scales as J α d − n with n = 9.5 ± 0.5. Previous measurements of 2-magnon excitations under pressure in NiO ( n ≈ 7–8), La 2 CuO 4 and Eu 2 CuO 4 ( n ≈ 5–6) are analyzed and an explanation for the trends in the pressure dependence of the superexchange interaction J is proposed.