Dilute Magnetic Alloys

Abstract

We shall devote a separate chapter to dilute “magnetic” alloys because both experimental results and theoretical approaches set such alloys apart from those discussed in Chapter 2. The adjective “magnetic” has been set in quotation marks because we do not refer here to magnetic systems in the conventional sense. On the contrary, we specifically exclude from discussion alloys which exhibit a phase transition to a magnetically ordered state, ferromagnetic or antiferromagnetic. Our interest is in alloy systems of nontransition-metal solvents with transition-metal or rare-earth solutes; moreover, the solute concentration is restricted to small values, typically less than a few tenths of an atomic percent and always less than a few atomic percent. The adjective “magnetic” arises from two sources: (a) First and foremost, there is the observation that the magnetic susceptibility of many such systems displays properties consistent with the presence of localized and free (or nearly free) magnetic moments, (b) There is a growing consensus that spin fluctuations are important for transport properties in many of these systems despite the apparent lack of significant temperature dependence in their magnetic susceptibilities. The concepts that have proved useful in understanding the properties of these alloys are also applicable to some alloys which do not require free magnetic moments or spin fluctuations being associated with solute atoms. Thus we shall include all these systems in our discussion.