Investigations of the atomic-scale structure of amorphous metallic alloys by means of bulk and local magnetic measurements

We review recent developments of magnetic studies oriented toward understanding of the atomic-scale structure of metallic amorphous alloys. First, we summarize the bulk magnetic measurements performed on glassy alloys containing Rare-Earths (RE) in a non-S ionic state. Provided that the RE content is low enough for the exchange effect to be negligible and for the local anisotropy manifestations to be regarded as single-ion effects, one can obtain some information about the average local symmetry and its distribution around a non-S RE ion in an amorphous matrix from the study of "crystal field". These electric field gradients are evidenced by the low-temperature behaviour of magnetic susceptibility, magnetization and calorimetric properties as well as by the depression of the critical temperature as a function of RE content in amorphous superconductors. Secondly, we review the informations which have been gained recently about the local symmetry in transition-metal base amorphous alloys by means of Mössbauer and NMR spectroscopy. An easy case is that of amorphous alloys of same composition as single-phase crystalline compounds. The local symmetry around the glass-former element is rather well preserved as compared with crystalline counterparts. The NMR technique is then able to yield an evaluation of the degree of randomness in various amorphous alloys and to separate the effects of structural and chemical disorder. The local symmetry about the transition metal sites is more complex and more widely distributed than about the glass - former sites. The complex nature of this short-range order can be more readily determined by studying the case of amorphous alloys whose composition differs from that of a stoichiometric crystalline compound. The special role played by the eutectic composition is discussed.