Impurity Magnons in MnF2:Ni

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Abstract
Fluorescence from the lowest spin orbital component of the 3T2 manifold of Ni ions in MnF2 is observed to terminate on the ground state 3A2 of the Ni with excitation of 0, 1, and 2 spin deviations centered on the nickel ion and corresponding, respectively, to the crystal ground state (G), and excitation of the s0 and s02 impurity magnon modes. Application of a magnetic field lifts the degeneracy of otherwise equivalent states of ions on different sublattices resulting in splittings of the ground and excited states. g factors and frequencies of these states were obtained by taking to second order the exchange off‐diagonal to the Ising‐Hamiltonian. gs02 ‐ gs0 and gG ‐ gs0 are predicted and found to have essentially the ionic Ni2+ g factor of 2.33 in agreement with that measured by ESR in ZnF2:Ni; magnetic field broadening of the ir s0f pair mode observed at 168 cm−1 is also as predicted. Frequencies of the three pair modes observed in Raman scattering and far ir absorption together with the s0 and s02 frequencies were computed to an accuracy of 0.5% or better by adjusting the impurity exchange integrals, J1′ = −1.1 cm−1 and J2′ = −3.41 cm−1.