Hyperf'meInteractions 24-26(1985)377- 393 377 SOME RECENT DEVELOPMENTS IN THE APPLICATION OF NUCLEAR MAGNETIC RESONANCE TO MAGNETICALLY ORDERED SYSTEMS J.I. BUDNICK Physics Department, Universityof Connecticut, Storrs, Connecticut 06268, USA and T.J. BURCH Physics Department, Marquette University,Milwaukee, Wisconsin53233, USA A brief outline of experimental results of NMR studies of ternary systems Fe3.xTxSi are presented. The observation of transition metal site selectivity, which correlates with electronegativity and atomic size, enables one to develop a quantitative model relating specific B sites and their corresponding near-neighbor moments. Brief reference is made to recent work on amorphous metals, short-range ordering, and the initial NMR studies of mulfilayer systems. 1. Introduction Ever since the first observation of nuclear magnetic resonance (NMR) in a metallic ferromagnet by Gossard and Portis [1], there has been a great interest in understanding the detailed excitation process for nuclei in domains and domain walls [2], and in the application of this spectroscopy to the study of hyperfine fields [3] and relaxation times [4] in magnetically ordered alloys. The relation of the results of hyperf'me field studies by both M6ssbauer and NMR to the promising neutron studies of the magnetic disturbance about an impurity in Fe by the Harwell group [5] provided an opportunity to construct a rather high-resolution picture for the effect of an im- purity and for the relationship, on a very local scale, between hyperfine fields deter- mined at specific near neighbors (NN) to the impurity [6] and the corresponding neutron deduced spatial variation of the local magnetization. Here one has the very complex theoretical problem of determining the separate long-range spin-up and spin- down polarizations produced by an impurity; a problem, similar to that of the con- duction electron polarization oscillations in a paramagnetic host [7], treated by Friedel and by the Ruderman, Kittel, Kasuya, and Yoshida approaches. For a review, see ref. [8]. Generally, the assignment of results of experimental data to a specific near neighbor has been complicated by the fact that in a binary disordered alloy one must 9J.C. BaltzerA.G., Scientific Publishing Company