Acoustic Paramagnetic Resonance of 3d Ions in KMgF3

Using an interference pulse‐echo technique at 9 GHz, we have observed acoustic paramagnetic resonance absorption and dispersion from the spin systems ${\mathrm{KMgF}}_3:{\mathrm{Ni}}^{\text{2+}}$ , ${\mathrm{KMgF}}_3:{\mathrm{Fe}}^{\text{2+}}$ and ${\mathrm{KMgF}}_3:{\mathrm{Co}}^{\text{2+}}$ , and have confirmed that, in the absence of saturation, the functions may be related quantitatively through the Kramers‐Kronig expressions. The moduli of the quadrupolar magnetoelastic coefficients ${\mathrm{|\hspace{0.17em}G}}_{11}\mathrm{\hspace{0.17em}|}$ and ${\mathrm{|\hspace{0.17em}G}}_{44}\mathrm{\hspace{0.17em}|}$ , for Ni²⁺ and Fe²⁺, were inferred to be 58 and 39, and 1340 and 1000 (cm⁻¹ unit strain⁻¹), respectively. For Co²⁺ we found the dipolar coefficients to be ${\mathrm{|\hspace{0.17em}F}}_{11}\text{\hspace{0.17em}|\hspace{0.17em}=\hspace{0.17em}64}$ and ${\mathrm{|\hspace{0.17em}F}}_{44}\text{\hspace{0.17em}|\hspace{0.17em}=\hspace{0.17em}35}$ (unit strain⁻¹). The observed angular dependence of the absorption in Co²⁺ cannot be accounted for by the simple spin‐lattice Hamiltonian. The experimental values of the magnetoelastic coefficients have been compared with point‐charge crystal field calculations.