Effect of high pressure and chemical substitution on the crystal structure and magnetic state of $\mathrm{R}_2\mathrm{Fe}_{17-x}\mathrm{Si}_x$ ($\mathrm{R}=\mathrm{Lu},\mathrm{Y}$; $x=0,1.7$)

The effect of high pressure on the crystal structure of the intermetallic compounds R₂Fe_{17 − x} Si_x (R = Lu or Y; x = 0 or 1.7) was studied using neutron diffraction. A correlation between changes in structural parameters and magnetic properties under the action of high pressure, as well as under chemical substitution of Si for Fe atoms, was analyzed in terms of localized moment and spin fluctuation models. The spin fluctuation model was found to describe more adequately the experimentally observed increase in the Curie temperature upon chemical substitution and the decrease in this temperature under the action of high pressure. Possible reasons for the suppression of a collinear ferromagnetic state and the occurrence of a noncollinear antiferromagnetic state in R₂Fe_17−x Si_x under pressure are discussed based on estimated differences between the total energy minima of these states.