Mapping the magnetization density near magnetic atoms in copper: Nuclear magnetic resonance studies of CuMn and CuCr

Using nuclear magnetic resonance, we have measured the magnetization density at the nuclear sites of several copper near neighbor shells surrounding the impurities manganese and chromium in the dilute alloys CuMn and CuCr. The resonances of these neighbor shells appear as weak "satellite" resonances near the iutense resonance produced by the majority of the copper nuclei which are far from any impurity. We have observed satellites for eight distinct shells in CuMn and six distinct shells in CuCr. These data are the first reported on satellites in CuCr and on all but three of the CuMn satellites. The magnetization density at each shell is directly proportional to the frequency shift of the resonances of that shell relative to the resonance of pure copper metal when observing at fixed magnetic field. Experiments are described on both powdered and single crystal alloy samples. The satellite signals are much stronger in powdered samples, but single crystals give more information. Powdered samples are used to find the satellites and measure the temperature dependence of their frequency shifts. To identify the shells producing the satellites, single crystals are necessary. Placing the applied field along three different crystal axes, we use the different symmetries of the shells with respect to the impurity atoms to make these identifications. From the CuMn data, we identify the satellites of the first four neighbor shells. For CuCr, we identify the satellites of shells one, three, and four and place a small upper limit on the shift of the second neighbor shell. In both alloys, the tensors describing the magnetic hyperfine and electric field gradient anisotropics are worked out for several shells. The map of the magnetization density made possible by the satellite identifications provides much more detailed information about the structure of these magnetic impurities than previously available. At high temperatures, we find the temperature dependence of the satellite shifts in CuCr differs from that expected from previous low temperature measurements of the magnetic susceptibility.U of I OnlyThesi