Thin Films and Surfaces



Heterogenous nucleation and growth


Catalysis on small particles


Thin Films


Heusler alloys

Heusler alloy Ni2MnIn

The intermetallic ternary compound Ni2MnIn is a Heusler alloy, named after F. Heusler1), who first described ferromagnetic manganese alloys in 1903 . Eigthy years later R.A. de Groot2) discovered that some of these alloys belong to a new class of magnetic materials which he called "half-magnetic ferromagnets". These materials share simultaneously the property of a semiconductor for the spin up electrons  and the property of a normal metal for the spin down electrons. Calculations of the density of states  show an energy gap between the valence and conduction bands for the minority-spin electrons and a continuous band for the majority electrons.

Fig. 1: Density of states calculated by K.A. Kilian et al.3).

Ni2MnIn seems to be promising as spin polarized electrode on InAs (001), becausse there is no Shottky barrier and virtually no lattice mismatch.
 
 

Preparation

The Ni2MnIn layers are grown by coevaporating the three compounds nickel, manganese and indium. The electron beam evaporator contains three independent, flux-controlled crucibles. As substrates we use InAs (001), silicon and thin carbon films which are heated during deposition. The layers on InAs and silicon substrates are structured by a lift-off process for further characterization of their electrical and magnetic properties.


Fig. 2: Omicron triple evaporator EMF3. A 50 nm thick Ni2MnIn film.


Characterization

The Ni2MnIn films on InAs and silicon substrate are analyzed in a scanning electron microscope (SEM), the layers on thin carbon films in a transmission electron microscope (TEM). In both electron microscopes we do energy dispersive analysis of X-rays in order to check the stoichometry. In addition, we gain information about the lattice constant by electron diffraction in the TEM. Film thickness and magnetization are measured by atomic force microscope (AFM) and magnetic force microscope (MFM), respectively.

Fig. 3: AFM image of a 50 nm thick film. Electron diffraction pattern.





Literature

1) F. Heusler, Verh. Dtsch. Ges. 5, 219 (1903)
2) R. A. de Groot et al., Phys. Rev. Lett. 50, 2024 (1983)
3) K. A. Kilian et al., IEEE Trans. on Magn. 37, 1976 (2001)


Last modified: 17/07/2002