Le Graët Chantal, de Vries Mark A, McLaren Mathew, Brydson Richard M D, Loving Melissa, Heiman Don, Lewis Laura H, Marrows Christopher H
School of Physics and Astronomy, University of Leeds.
J Vis Exp. 2013 Oct 5(80):50603. doi: 10.3791/50603.
Chemically ordered alloys are useful in a variety of magnetic nanotechnologies. They are most conveniently prepared at an industrial scale using sputtering techniques. Here we describe a method for preparing epitaxial thin films of B2-ordered FeRh by sputter deposition onto single crystal MgO substrates. Deposition at a slow rate onto a heated substrate allows time for the adatoms to both settle into a lattice with a well-defined epitaxial relationship with the substrate and also to find their proper places in the Fe and Rh sublattices of the B2 structure. The structure is conveniently characterized with X-ray reflectometry and diffraction and can be visualised directly using transmission electron micrograph cross-sections. B2-ordered FeRh exhibits an unusual metamagnetic phase transition: the ground state is antiferromagnetic but the alloy transforms into a ferromagnet on heating with a typical transition temperature of about 380 K. This is accompanied by a 1% volume expansion of the unit cell: isotropic in bulk, but laterally clamped in an epilayer. The presence of the antiferromagnetic ground state and the associated first order phase transition is very sensitive to the correct equiatomic stoichiometry and proper B2 ordering, and so is a convenient means to demonstrate the quality of the layers that can be deposited with this approach. We also give some examples of the various techniques by which the change in phase can be detected.
化学有序合金在多种磁性纳米技术中很有用。使用溅射技术以工业规模制备它们最为方便。在此，我们描述一种通过溅射沉积在单晶氧化镁衬底上制备B2有序FeRh外延薄膜的方法。以缓慢速率沉积到加热的衬底上，使吸附原子有时间既沉淀到与衬底具有明确外延关系的晶格中，又能在B2结构的Fe和Rh子晶格中找到它们的合适位置。该结构可用X射线反射测量法和衍射方便地进行表征，并且可以使用透射电子显微镜截面直接可视化。B2有序FeRh表现出一种不寻常的变磁相变：基态是反铁磁性的，但合金在加热时转变为铁磁性，典型转变温度约为380K。这伴随着晶胞1%的体积膨胀：在体相中是各向同性的，但在外延层中横向受到限制。反铁磁性基态和相关的一级相变的存在对正确的等原子化学计量比和适当的B2有序非常敏感，因此是一种方便的手段来证明用这种方法可以沉积的层的质量。我们还给出了一些可用于检测相变的各种技术的示例。
