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Floating zone growth of Co2Cr1-xFexAl  Heusler compounds

Ahmad Omar ,  Maria Dimitrakopoulou ,  Christian G F. Blum ,  Horst Wendrock ,  Steven Rodan ,  Silke Hampel ,  Wolfgang Löser ,  Bernd Büchner ,  Sabine Wurmehl 

Leibniz-Institute for Solid State and Materials Research, P.O.Box 270116, Dresden D-01171, Germany

Abstract

Many Heusler compounds are predicted to be half-metallic ferromagnets and find extensive interest as materials for spintronic applications, an example of which is the Co2Cr1-xFexAl  series. So far, bulk samples of that series, in particular Cr-rich samples, do not verify those predictions and various studies yield results which are fraught with anomalies. Thin films as well do not meet the expectations in magnetoresistance ratio nor in degree of spin polarization and magnetic moments. In the present work, crystal growth of Co2Cr1-xFexAl  Heusler compounds has been done, as a step towards understanding the intrinsic material properties of this series. To begin with, polycrystalline samples of Co2CrAl, Co2FeAl and Co2Cr0.6Fe0.4Al were prepared and found to be phase segregated, a hurdle already reported and easily tackled by using the Optical Floating Zone technique (FZ). Our results demonstrate that, although this phase segregation is eliminated in the FZ grown samples, an unexpected phase transformation via spinodal decomposition is taking place in samples containing Cr. This phase decomposition is found to strongly affect the magnetic properties and hence also other properties as e.g. the spin polarization. Our finding presents new insight into the phase dynamics in this system and provides answers to many of the issues in this series of half-metallic ferromagnets.

 

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Related papers

Presentation: Poster at 15th Summer School on Crystal Growth - ISSCG-15, by Ahmad Omar
See On-line Journal of 15th Summer School on Crystal Growth - ISSCG-15

Submitted: 2013-06-14 10:04
Revised:   2013-06-14 10:04