The present work constitutes a part of a continuing series of studies dealing with models, in which only the two lowest levels of the crystal field splitting scheme of the Pr3+ ion in P r intermetallics are retained. Taking into account the magnetic state equations derived from a model, in which the ground and first excited levels are doublet and triplet, respectively, the existence of a gap between the para-and ferromagnetic phases is shown in the space of J,, (effective exchange parameter) versus d (crystal field parameter). This study is applied to the available experimental data of several Pr intermetallics, in cubic symmetry, and the results are in line with the previsions of the model.Ce present travail fait parti d'une serit d'btudes concernant nos modeles, dans lesquels nous retenons seulement les deux niveaux inftrieurs du schtma du stparation de champ cristallin de I'ion Pr3+ en Pr intermttallique. Considtrant les tquations des ttats magnbtiques derivees du modele, dans lequel le niveaux fondamental et le premier niveaux d'excitation sont respectivement double et triple, il est dkmontrte l'existance d'une lacune entre les phases para-et ferromagnetique dans l'espace de Jo (paramhtre d'kchange effectif) contre d (parametre du champ cristallin). Cette etude a Ctt appliqute 9 diffkrents valeurs expkrimentales disponibles du "Pr intermetallique", en symetrie cubique. Les rtsultats sont en accord avec les previsions du modele.
The magnetic behavior of a model in which van Vleck ions, under the action of a crystal field, interacting by exchange with an electron gas is investigated. The condition of onset of ferromagnetism and the behavior of the critical temperature, band and ionic magnetizations (and susceptibilities) versus temperature, as a function of the band width, exchange interaction, and the crystal field splitting energy parameters are obtained within an approximation equivalent to a molecular field formulation.On a ktudib le comportement magnktique d'un mod81e dans lequel des ions van Vleck, sous I'action d'un champ cristallin, interagent par kchange avec un gas d'8lectrons. On a obtenu la condition d'existence d'ordre ferromagnktique, la dependence avec la tempbrature de l'aimantation e t de la susceptibilitk ainsi que la tempkrature critique en fouction de la largeur de bande e t des paramktres du champ cristallin e t d'kchange dans une approximation de champ molkculaire.
In order to study the magnetism of rare-earth (RE) intermetallics, we must consider simultaneously the crystal field (CF) and magnetic interactions.In the description of the magnetic interaction associated with the RE intermetallic, we must take into account that the 4f electrons of a RE ion are strongly localized and the overlap between 4f orbitals is negligible, so that the direct exchange can be ruled out. In this case the indirect exchange via conduction electrons which is of RKKY type l l / , becomes important and mainly characterizes the magnetic behaviour of RE metals. In the first approximation considering the conduction electrons to be purely itinerants, the coupling between ions i and j will be represented by the isotropic Heisenberg exchange.The CF interaction of these compounds has been treated in the literature taking the ground multiplet of the CF splitting of a R E ion corresponding to a RE intermetallic in an integral way and the CF Hamiltonian has been generally described through Stevens' operators I 2 1 using the Lea-Leask-Wolf notation 131.In this note, we are proposing a model in which we keep only the two lowest levels of the split 4f shell of the R E ion in the study of the CF and magnetic interactions. This approach provides an appropriate theoretical framework for studying the magnetic properties of many R E intermetallics since the highly relevant results of this study are obtained a t low temperatures. The main advantage of the two level models is that they simplify the description of the above-mentioned interactions, providing simple magnetic state equations from which we can obtain the adequate value of the Land6 factor and effective exchange parameter for each RE intermetallic. This may be accomplished putting into these equations the suitable experimental data of the magnetic and crystallographic quantities given in the literature. I ) 24.020 -Niteroi, R J Brazil. ') 20.550 -Rio de Janeiro, R J Brazil. ') 22.723 -Rio de Janeiro, R J Brazil.
BYApplication to PrAlz L. PALERMO (a) and X. A. DA SILVA (b) The magnetization, susceptibility, and magnetic specific heat of PrAI, versus temperature are studied within a model where the onset of magnetism is due to the mutual magnetization of rareearth ions and conduction electrons, and the ionic magnetization process is van Vleck-like. The crystal field, bandwidth, and exchange parameters of the model which fit the available experimental data are 2.5, 7000, and 341 meV, respectively.On Btudie la magnbtization, la siisceptibilitb e t la chaleur specifique magnbtique de PrAI, versus tempbrature dans un modble oh I'ordre magnetique est due B la magnbtization mutuelle des ions e t des Blectrons de conduction, la magnBtization ionique Atant du type van Vleck. Le champ cristallin, la largeur de bande et le parametre d'hchange d u modele en accord avec les donnkes experimentaux sont 2,5; 7000 e t 341 meV, respectivement.
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