Recently, a new lab building was constructed that will host the fabrication and characterization tools for the Heusler thin films in the near future. The long term perspective is to cluster different preparation techniques (magnetorn sputtering, pulsed laser deposition and molecular beam epitaxie) and surface sensitive probing methods (XPS, STM, AFM, ...) to study high quality samples without breaking the vacuum.
The fabrication and characterisation for proving the predicted properties of Heusler compounds can often be very challenging. The control of atomic order, interfaces, and surfaces plays an important role. Recently, Jourdan et al. showed for the first time the predicted half-metallic character of the Heusler compound Co2MnSi measured at room temperature by in situ spin-resolved ultraviolet photoemission spectroscopy. These experiments clearly emphasise the importance of careful thin film preparation and in situ characterisation that can indeed result in a high spin polarisation. Furthermore, they show that the observed low TMR ratios are not limited by the intrinsic spin polarisation of the Heusler alloy (here Co2MnSi) and that much higher values can be expected for carefully grown MTJs containing Heusler compounds. If atomic ordering, interface defects and termination, and the barrier are well controlled, high TMR ratios of about 2000% (330% at room temperature) can be realised, as demonstrated by Liu et al.
For these purposes, we have built a state-of-the-art UHV cluster tool for Heusler thin film fabrication and analysis that is hosted in a recently constructed new lab building. The cluster also allows us to characterise Heusler bulk samples and to utilise them as substrates. The complete system of our setup together with the laboratory layout is depicted in Figure 1. The layout of the laboratory is adopted from a typical cleanroom and offers a separated double door system for changing shoes and a technical room that houses roughing pumps, gas cabinets, and cryo pumps. The main laboratory is equipped with a raised floor (colored as periodic table), which also acts as the inlet for the air conditioning system. All needed media such as cooling water, power, and gas lines are installed below this floor. The benches and hoods in the upper right corner of Figure 1 are dedicated for cleaning or wet etching of wafers and substrates. The individual units of the cluster are described in their sections of the left menu.