EPR Determination of the Nearest-Neighbor Exchange Constant for Mn2+ Pairs in KZnF3

Abstract

The electron paramagnetic resonance of exchange‐coupled pairs of Mn²⁺ ions has been observed in Mn²⁺ doped KZnF₃, a cubic perovskite. The Mn/Zn ratio used was approximately 0.01. The angular dependence of the pair spectrum indicates that the pair axes are along the three equivalent 〈100〉 directions. Thus the pairs are nearest magnetic neighbors and are expected to be antiferromagnetically coupled. At 4.2°K, only the S = 1 and S = 0 states are significantly occupied and the spectrum which arises from pairs in the S = 1 state is adequately explained by the spin Hamiltonian

$$\mathcal{H}\mathrm{=g\beta }\mathrm{H}·\mathrm{S}{\mathrm{+DS}}_z^2\mathrm{+AS·(}{\mathrm{I}}_1+{\mathrm{I}}_2)$$

, with g = 2.004, | D | = 2.996 kG. From the linewidths of the unresolved hyperfine sets, A∼50 G is found. For a nn Mn²⁺ pair separated by the normal Zn–Zn distance (4.06 Å) in KZnF₃, the dipolar contribution is expected to be D = −3.11 kG, indicating that any local distortion is small. From the temperature dependence of the S = 1 lines in the region 1.5°–25°K, the exchange constant $J_{\mathrm{nn}}\mathrm{\hspace{0.17em}(}{\mathcal{H}}_{\mathrm{ex}}\mathrm{=J}{\mathrm{S}}_1·{\mathrm{S}}_2)$ is found to be +9.9°±0.6°K. This is compared with macroscopic measurements of J in antiferromagnetic KMnF₃ and optical measurements in KZnF₃:Mn.