(Eu,Gd)Te - MBE Growth and Characterization

Abstract

Monocrystalline thin layers of (Eu,Gd)Te, n-type ferromagnetic semiconductor, were grown by molecular beam epitaxy technique on BaF2 (111) substrates. Reflection high-energy electron diffraction, X-ray diffraction, and atomic force microscopy characterization proved epitaxial mode of growth and high crystal quality of the layers. Magnetic susceptibility and magnetic resonance measurements showed that in (Eu,Gd)Te layers ferromagnetic transition takes place at about 13 K. Electrical characterization carried out by the Hall effect and resistivity measurements revealed very high electron concentration of 10 20 cm −3 and sharp maximum of resistivity at transition temperature.

Ferromagnetic (Eu,Gd)Te/PbTe semiconductor heterostructures

“…A maximum was observed in the temperature dependence of resistivity at the Curie temperature directly showing a correlated behaviour of magnetic and electrical properties of n-(Eu,Gd)Te layers. These layers exhibit also negative magnetoresistance (over 90% at magnetic field of 10 T at temperatures below and close to T C ) related to the suppression by external magnetic field of the scattering on magnetic ions [7].…”

“…The intensity oscillations of the RHEED specular spot allowed to determine the rates of growth as equal to 0.1 ML/s for (Eu,Gd)Te and 0.6 ML/s for PbTe (ML is monolayer thickness). The MBE growth conditions for (Eu,Gd)Te layers are discussed in more detail in [7].…”

“…The control of Te molecular flux and substrate temperature can dramatically change electrical and magnetic properties of (Eu,Gd)Te. The growth of the layers with composition far from stoichiometric (with excess of Te) leads to the compensation of the n-type conductivity in (Eu,Gd)Te due to the formation of other Gd-Te complexes with varying Gd valency [7,8]. It results in insulating (Eu,Gd)Te layers exhibiting no ferromagnetic transition [7].…”

“…The growth of the layers with composition far from stoichiometric (with excess of Te) leads to the compensation of the n-type conductivity in (Eu,Gd)Te due to the formation of other Gd-Te complexes with varying Gd valency [7,8]. It results in insulating (Eu,Gd)Te layers exhibiting no ferromagnetic transition [7]. In the case of PbTe layers, the stoichiometry engineering is the well known method for controlling their electrical properties, in particular PbTe with slightly excess Te is p-type material.…”