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Showing papers by "Chalk River Laboratories published in 1971"


Journal ArticleDOI
TL;DR: In this paper, the theory of low lying magnetic excitations of KCoF3 is developed and the parameters describing the magnetic interactions are obtained by comparison with the experimental results of the previous paper.
Abstract: For Pt. I see ibid. vol. 4, 2127. The theory of the low lying magnetic excitations of KCoF3 is developed and the parameters describing the magnetic interactions are obtained by comparison with the experimental results of the previous paper. The branch of the elementary excitation spectrum of lowest frequency is well described by a phenomenological model with an effective spin s'=1/2. The exchange interaction has the Heisenberg form, and the pseudo-dipolar form of anisotropic exchange proposed for KCoF3 is shown to be less than 8% of the isotropic exchange. A model which takes the orbital angular momentum of the Co2+ ion into account is developed by relating the elementary excitations to the quasiboson excitations between the ground state and all eleven excited states of the 4T1 orbital level. This model fits the experimental results for the two branches of lowest frequency extremely well. The interaction between real spins is found to of the Heisenberg form and the spin-orbit coupling constant is found to be 82% of the free ion value. Calculations of the relative intensity of neutron scattering as a function of wavevector transfer for the modes belonging to the two lowest branches of magnetic excitations give good agreement with experiment.

90 citations


Journal ArticleDOI
TL;DR: In this paper, the magnon-phonon interaction was found to be 0.35+or-0.10 THz and from the temperature dependence of the modes, it was shown that magnon and phonon interaction is appreciable only within a radius 0.2*2 pi /a of the magnetic zone centre.
Abstract: Dispersion curves for magnons and phonons propagating in KCoF3 at low temperatures have been determined by means of neutron inelastic scattering techniques. Two branches of magnetic excitations have been observed corresponding to a transition between the two members of the ground state doublet (j=1/2) of the Co2+ ion and a transition between the ground state and the lowest member of the j=3/2 spin-orbit level. Neither branch shows evidence for the directional anisotropy which has been suggested for the exchange interactions in KCoF3; any splitting of the doubly degenerate magnon branch is shown to be less than 8% in frequency. The magnon branch of lowest frequency interacts with a phonon branch in the vicinity of the magnetic zone centre. The strength of the magnon-phonon interaction is found to be 0.35+or-0.10 THz and from the temperature dependence of the modes the magnon-phonon interaction is shown to be appreciable only within a radius 0.2*2 pi /a of the magnetic zone centre. The magnetic modes of higher frequency show a market decrease in intensity with increasing temperature but little change in frequency in accordance with expectations for a transition that depends strongly on the spin-orbit coupling but only weakly on the exchange.

45 citations


Journal ArticleDOI
TL;DR: In this paper, a version of the intermediate coupling vibrational model, in which quasiparticle and anharmonic core effects are considered, is described, and a detailed application of the model to A = 33 and 34 nuclei is presented.

44 citations