1. INTRODUCTION

Magnetic thin films have provided a highly successful test ground for understanding the microscopic mechanisms which determine macroscopically observable quantitities like the magnetization vector, different types of magnetic order (ferro-, ferri- and antiferromagnetism), magnetic anisotropy and ordering temperatures (Curie, N el temperature). The success has been based on the simultaneous development of the following techniques: a) the preparation of single crystalline mono- and multilayers on different types of substrates in ultrahigh vacuum systems, b) the development of vacuum compatible, monolayer-sensitive magnetic analysis techniques, c) the advance in computing power to provide first-principles calculations of magnetic ground state properties. Aside from these basic research orientated investigations the technological exploitation of thin film magnetism has lead to huge increases in the hard disk's magnetic data storage capacities and new types of magneto-resistive angle and position sensitive sensors in the automotive industry, for example.

The purpose of this chapter is threefold: a) An introductory level overview about basic physics in thin film magnetism will be given, b) characteristic examples of current research using synchrotron radiation , SQUID and magnetic resonance techniques will be discussed.

Various aspects of ultrathin film magnetism have been discussed in extensive reviews and book chapters over the last few years (see for example refs. 1 9) There is no way to summarize all these issues in such limited space and the reader is referred to the reviews mentioned before. The examples which I will discuss here are strictly restricted to the thickness and temperature dependent magnetic...