Ionic model for chromium, manganese and iron impurities in copper
We have discovered that the NMR frequencies of Cu atoms which are near neighbors to Cr atoms in dilute CuCr have an anomolous temperature dependence. Comparison with data from CuMn and CuFe which display the normal temperature dependence of a Curie-Weiss law lead us to conclude that an ionic model of the magnetic impurity is necessary to explain the data. We develop a model which assumes a definite 3dn configuration with a definite L-S ground state and includes intraconfigurationa1 energy level splittings due to a crystalline electric field and spin-orbit coupling. We calculate the spin and orbital susceptibilities from the ionic structure and include the effects of the impurity electron-conduction electron mixing interaction in a perturbation treatment. We also calculate the impurity hyperfine fields expected from the mode1+ Comparison of the model predictions with the data lead us to conclude that (a) Cr and Mn have the structure which corresponds to the free ion divalent configuration while Fe corresponds to a monovalent configuration, (b) the crystal field at the site of the magnetic atoms is opposite of that usually assumed, and (c) the Weiss temperature of CuCr is 2.9 ±l.O K which is higher than most previously reported values but agrees within the experimental errors with a recently published bulk magnetic susceptibility measurement.
ionic model, chromium, manganese, iron, copper, Curie-Weiss law, magnetic impurity
University of Illinois - Urbana-Champaign
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