Effective interatomic forces from one‐particle crystal field parameters

Abstract

BY8. ADAM3) (a), GH. AD AM^) (a), and A. CORCIOVEI (b) Theoretical results are obtained for the crystal field coefficients which enable us t o develop an approach to the use of the crystal field data for the derivation of information on the effective interatomic forces in crystals. The method is applied to the magnetic SmS+ ion in SmCo,, and it is shown to provide valuable results both for the effective interatomic potential and for the consistency of various sets of crystal field parameters previously proposed in the literature.Des rbsultats sont obtenus pour les coefficients du champ cristallin qui nous permettent de dbvelopper me mbthode pour la dktermination des forces uniparticule dans un cristal en utilisant les donnbes expbrimentales pour le champ cristallin. La mbthode est appliquQ L I'ion magnbtique SmS+ en SmCo,. Elle s'avhre capable de fournir tant des rbsultats pour le potentiel uniparticule effectif que des indications concernant la consistance des divers sets de parambtres du champ cristnllin proposbs antbrieurement dans la IitGrature. IntroductionI n a recent paper [l], which will be quoted henceforth as I, the one-particle crystal field experienced by f electrons of magnetic ions within crystals has been derived under the general assumption of arbitrary (possibly noncentral, as, e.g., in the covalent crystals) effective interatomic forces.I n the present paper, assuming centrul one-particle effective interatomic forces (a hypothesis which is known t o hold, e.g., for metallic systems), we first push the argument of I a step further and derive, in Section 2, more explicit expressions for the coefficients of the crystal field occurring both in cubic and hexagonal compounds. The simplicity of Stevens' standard expression for the crystal field coefficients, A , ( r m ) , (Stevens [2], Hutchings [3], Abragam and Bleaney [4]) is shown to be preserved with, however, the terms of the product specifically renormalized by the non-Coulombian interaction.Then, inverting the argument, we show, in Section 3, that the experimental knowledge of the crystal field coefficients enables us to get valuable insight into the spatial behaviour of the one-particle forces that govern t,he interaction between the magnetic electrons and the crystal lattice within monocrystalline samples.The general procedure of Section 3 is applied, in Section 4, to the magnetic Sm3f ion in SmCo,. Amongst the data previously proposed in the literature for the crystal field coefficients in SmCo, (Sankar et al.