ENDOR Study of the Unpaired Spin Density in KZnF3:Mn2+

Abstract

ENDOR techniques were used on KZnF₃:Mn²⁺ to investigate spin polarization of the electrons which contribute to nearest‐ and next‐nearest neighbor Mn²⁺ superexchange interactions in the anti‐ferromagnetic isomorph, KMnF₃. Spin unpairing contributes measurably to the superhyperfine (shf) interaction with 1st and 2nd‐nearest fluorine neighbors of Mn²⁺ ions in KZnF₃. The shf constants at 4.2°K for the 1st neighbor F⁻ nuclei are A_s=54.26±0.03 MHz and A_σ−A_π=0.68±0.03 MHz, using r=2.065 Å for the Mn²⁺–F⁻ separation. From the above results the fraction of unpaired spin in the 2s and 2p orbitals of these F⁻ ions is calculated to be f_s=0.60% and f_σ−f_π=0.26%. For the 2nd neighbor F nuclei at (a₀/2, 0, a₀), a₀ being the lattice constant, we find the components of the shf tensor (in MHz) to be B_xx=0.38, B_yy=−0.30, B_zz=1.60, ½(B_xz+B_zx) = 1.04, with B_zx≅B_xz. These values reflect an isotropic component B_s=0.56 MHz which is 2.5 times larger than that found by Davies in the less covalent salt KMgF₃:Mn²⁺. This indicates the importance of covalency (as opposed to overlap) contributions to the spin unpairing at more distant neighbors of Mn²⁺ ions in perovskite fluorides.