Surface-driven magnetism in ultrathin ferromagnetic and antiferromagnetic films

常规材料的超薄(2至10个原子层)薄膜的材料性质往往是非常规的。这可能是因为这些薄膜采用了非常规的结构，因为它们作为二维而不是三维系统，因为表面起着重要的作用，或者因为其他原因。例如，研究铁和镍等传统磁性材料的超薄膜的磁性就是一个很好的例子，在那里观察到了一些以前不为人知的磁性现象，其中一些导致了在磁数据存储和检索方面的应用。这项提议旨在研究超薄磁性薄膜的两个主要概念。第一个是继续我们对铁薄膜中从磁态到非磁态的转变的研究。第二个是研究如何在二维材料中发生这种转变的基本问题。第二个是学习如何生长反铁磁性薄膜--即每个原子的磁矩相对排列的薄膜。这种状态在块状晶体中是众所周知的，但目前，没有简单的方法可以在超薄膜中检测到它。我们建议改进光磁响应技术，使这些测量成为可能，并为这类难以捉摸的材料打开一扇窗。

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.