Structural, Electronic, and Magnetic Properties of Thin Films and Superlattices
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TIN/SEPTEMBER1990
ment has been an essential élément in the phénoménal growth in this area of materials science. More specifically, the advent of accurate self-consistent (local) spin density functional (LSDF) calculations for surfaces, interfaces, and multilayers means that theory is no longer limited to simple, parameter-dependent models. Thèse complex Systems are of growing interest because the reduced symmetry, lower coordination number, and availability and rôle of highly localized surface and interface states offers the possibility of inducing new and exotic phenomena and promûtes the possibility of new device applications. We will describe how first principles methods are being used to obtain structural, electronic, and magnetic properties, and how thèse calculations can give not only a clearer understanding of the expérimental results but also prédictions on novel Systems that are not yet made experimentally. The range and variety of materials under investigation are enormous. One of the récent i m p o r t a n t d e v e l o p i n g trends lies in the préparation of synthetic structures on the submicron level, which will permit in the near future new scientific phenomena to be investigated and novel device applications to be developed on artificially made materials not found in nature. In addition to
the technological reasons for focusing attention on submicron problems, there are interesting p h e n o m e n a to study which, themselves, are of fundamental and physical interest. Indeed, our own scientific attention has spread from considération of bulk properties to obtaining a better fundamental understanding of reduced-dimensionality-phenomena at surfaces and interfaces. The kinds of answers that this type of approach can give are broad and include quantifies that are experimentally accessible (such as density of states, magnetic moments, and energy level transitions), as well as some that are not (such as inlayer bond-length relaxations) and yet still important in affecting the overall properties of a given material. Of course, when direct comparisons are available, they provide powerful methods to test theoretical calculations and eventually to improve them. In the following, we will limit our discussion to only a few selected examples taken from the several différent Systems we hâve recently been studying. Our goal is to provide a gênerai overview of the complexity of the différent issues involved and, at the same rime, to illustrate the kind of answers that our theoreticalcomputational approach can offer to the understanding of thèse issues by yielding well-defined results and making précise prédictions. Various examples hâve demonstrated that it is possible not only to make quantitative prédictions for real Systems, but more importantly, to gain insights into the underlying physics of thèse materials, which are essential for the pure science and also for potenrial device applications. M e t h o d o l o g y and Approach Since many of the p h e n o m e n a are directly related to the electronic structur
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