Fedro, Arthur J.||Shaffer, John C., 1938-2017||Kimball, Clyde W.
M.S. (Master of Science)
Department of Physics
Copper compounds||Magnetism||Terbium compounds
The metamagnetic TbCu? compound exhibits a magnetic structure in zero magnetic field that can be interpreted with remarkable accuracy by using Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. In this work we have investigated the behavior of the effective direct exchange coupling under the variation of the character of the atomic wave function and obtained a long range oscillatory function for J(R) vs. R similar to that in standard RKKY theory. The computation of the molecular field exchange parameters was also carried out by choosing a simple but not perfectly spherical model for the Fermi surface, i.e., considering the Fermi momentum k[sub F] as an adjustable parameter. Another approach was to vary the parameter q[sub o] (reflecting the shape of the 4f wave function) and use the standard value of k[sub F]. Either of the above two approaches was found to be good enough to give the predicted results for molecular field exchange parameters, ?' and ?". But, the latter was ruled out because the variation of q[sub o] seems physically meaningless. Enlargement of Fermi radius by 10% resulted in positive ?' and ?" with the stability conditions satisfied. This calculation stresses the physically reasonable long range character of the direct exchange coupling and is in contrast to a similar molecular field treatment of Kouvel et al. using a short range interaction, i.e., they assume only first and second nearest neighbors interact. We find though that we match up with experiment results only through the Introduction of one ion anisotropy energy term. However, this anisotropy energy has no effect on the stability condition.
Afshar, Fatimah, "Analysis of magnetic structure of TbCu? using the RKKY formalism" (1972). Graduate Research Theses & Dissertations. 1458.
Northern Illinois University
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