Surface-driven magnetism in ultrathin ferromagnetic and antiferromagnetic films

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The materials properties of extremely thin (2 to 10 atom layers) films of conventional materials are often unconventional.  This can be because these films take an unconventional structure, because they act as 2-dimensional rather than 3-dimensional systems, because surfaces play an important role, or because of other reasons.  The investigation of the magnetic properties of ultrathin films of conventional magnetic materials such as iron and nickel is an excellent example, where a number of previously unknown magnetic phenomena have been observed, some of them leading to applications in magnetic data storage and retrieval. This proposal aims to investigate two main ideas in the context of ultrathin magnetic films.  The first is to continue our studies of the transition from the magnetic state to the non-magnetic state in iron films.  This work addresses fundamental questions concerning how this transition occurs in a 2-dimensional material.  The second is to learn how to grow antiferromagnetic films -- i.e. films where the magnetic moment of every other atom is aligned oppositely.  This state is well known in bulk crystals, but at present, there is no simple way to detect it in ultrathin films.  We propose to refine optical magnetic response techniques to allow these measurements, and to open a window on this elusive class of materials.