Volume dependence of magnetic hyperfine fields in Eu-intermetallic compounds

High-pressure M\"ossbauer studies on ¹⁵¹Eu intermetallics (EuAl₂, EuAl₄, EuCu₂, EuCu₅, EuSn₃, Eu0.5{Yb}0.5Sn₃, EuZn₂, and EuPt₂) provide information about the volume dependence of the effective hyperfine field Beff at the Eu²⁺ nucleus. These measurements have been performed at 4.2 K and pressures up to 65 kbar. The results show that (i) the volume dependence of the transferred hyperfine field Bthf is the dominating contribution to ∂Beff∂lnV; (ii) the magnitude of ∂Bthf∂lnV can be explained only if one assumes the participation of s, p, and d conduction electrons in the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction responsible for Bthf; and (iii) the exchange integrals for non-s conduction electrons (Jp,f and/or Jd,f) are more sensitive to volume changes than that for s conduction electrons (Js,f).