Quality of Heusler Single Crystals Examined by Depth Dependent Positron Annihilation Techniques

TL;DR

This study investigates the electronic structure and defect characteristics of Heusler single crystals using depth-dependent positron annihilation techniques, highlighting recent progress in crystal growth and analysis methods.

Contribution

It demonstrates the application of ACAR and DBS techniques to analyze Heusler crystals, revealing Fermi surface anisotropy and defect concentrations for the first time.

Findings

Clear Fermi surface anisotropy observed in Cu2MnAl

Fe2TiSn spectra affected by foreign phases

Positron diffusion length used to estimate defect levels

Abstract

Heusler compounds exhibit a wide range of different electronic ground states and are hence expected to be applicable as functional materials in novel electronic and spintronic devices. Since the growth of large and defect-free Heusler crystals is still challenging, single crystals of Fe2TiSn and Cu2MnAl were grown by the optical floating zone technique. Two positron annihilation techniques -Angular Correlation of Annihilation Radiation (ACAR) and Doppler Broadening Spectroscopy (DBS)- were applied in order to study both, the electronic structure and lattice defects. Recently, we succeeded to observe clearly the anisotropy of the Fermi surface of Cu2MnAl, whereas the spectra of Fe2TiSn were disturbed by foreign phases. In order to estimate the defect concentration in different samples of Heusler compounds the positron diffusion length was determined by DBS using a monoenergetic positron beam.