Films of Heusler alloys

Heusler alloys (HA) are a class of materials which may be metals, semiconductors or semimetals, most of them being ferromagnets. Some new applications of HA in spintronics and micro-electromagnetic actuators require their preparation in the form of thin films. Deposition of a HA film is a challenging task from the point of view of its proper ordering. Local disorder and antisite disorder are the most probable reasons of failure in achieving 100% polarization in nanostructures containing HA layers. We will review some examples of tunnel magnetoresistance structures that include Co2YZ HA layers (Y = Mn, Cr, Fe, Z = Al, Si, Ga). The influence of structural ordering on the magnetic and transport properties of Co2MnGa films are given with an emphasis on crystallization process of the films with amorphous structure and a further improvement of its structural ordering. Equally difficult task concerns preparation of HA films with shape memory (SM) effect. Recent achievements in technology of HA with SM will be reviewed. We will focus on non-stoichiometric Ni-Mn-Ga sputtered films. Their SM properties critically depend on composition and post-deposition annealing conditions. By a proper choice of these conditions, the ordered Ni-Mn-Ga films exhibit a well defined SM effect near room temperature.