EFFECT OF PRESSURE ON 2-MAGNON RAMAN-SCATTERING IN K2NIF4

We measured the effect of pressure (P less-than-or-equal-to 10 GPa) on 2-magnon excitations (T = 10 K) and on lattice parameters (T = 300 K) of K2NiF4 by Raman spectroscopy and X-ray diffraction respectively. T he results allow us to determine the dependence of the superexchange i nteraction J on the transition metal to anion distance d. We find that J scales as J is-proportional-to d(-n) with n = 9.5 +/- 0.5. Previous measurements of 2-magnon excitations under pressure in NiO (n almost- equal-to 7-8), La2CuO4 and Eu2CuO4 (n almost-equal-to 5-6) are analyze d and an explanation for the trends in the pressure dependence of the superexchange interaction J is proposed.