Domain Hyperfine Fields in Some Dilute Ferromagnetic Alloys Studied by NMR on Oriented Nuclei.

摘要

Hyperfine field distributions at the sites of exp 60Co atoms dissolved in some dilute (up to 4percent) CoFe and NiFe alloys were measured by NMR on oriented nuclei at very low temperatures. The hyperfine field shifts due to neighboring impurities are shown to be consistent with a model in which the shifts are caused by moment perturbations in the neighboring shells surrounding an impurity,with RKKY-like spin density oscillations affecting the conduction electron and core polarization contributions to the hyperfine field. The observed shifts at a exp 60Co site are +1.86 +- 0.22kG with a nearest neighbor substituent Co, -4.28 +- 0.17kG with a second nearest neighbor substituent, -3.41 +- 0.07kG for a third nearest neighbor substituent and -0.98 +- 0.05kG for a fourth nearest neighbor substituent. In the NiFe alloys,the shifts are -3.48 +- 0.23kG, -6.63 +- 0.14kg, -5.14 +- 0.25kG,and -1.49 +- 0.14kG respectively for Ni neighbors. The shifts are shown to be generally smaller than those at the Fe sites,the trends being consistent with a reduced number of itinerant electrons in going across the 3d transition series and with the moment perturbations arising via the itinerant d's. Small quadrupole contributions to the hyperfine interactions are shown to exist by the response in adiabatic fast passage resonance sweeps,but do not contribute significantly to the magnetic resonance lineshapes. exp 60Co spin-lattice relaxation times were measured for the main and satellite resonances in some CoFe alloys and no statistically significant changes in a function of alloy concentration or the sub-resonance excited were observed. (ERA citation 01:026074)