Unveiling the structure-property relationship in metastable Heusler compounds by systematic disorder tuning

Abstract

Heusler compounds represent a unique class of materials that exhibit a wide range of fascinating and tuneable properties such as exotic magnetic phases, superconductivity, band topology or thermoelectricity. An exceptional, but for Heusler compounds common feature is that they are prone to antisite defects and disorder. In this regard, the Fe2VAl Heusler compound has been a particularly interesting and disputed candidate. Even though, various theoretical scenarios for the interplay of physical properties and disorder have been proposed, the metastable disordered A2 phase hitherto precluded experimental investigation in bulk samples. Here, we report experimental results on disorder-tuned Fe2VAl0.9Si0.1 alloys all the way towards the A2 phase, which we realized via rapidly quenching our samples from high temperatures. We measured the thermoelectric properties of these materials in a wide temperature range (4 to 700 K), which suggest a gradual semimetal/narrow-gap semiconductor → metal transition upon increasing the disorder. We also find a large anomalous Hall effect in the disordered A2 phase, arising from the side-jump scattering of charge carriers at the antisite magnetic moments. This is corroborated by measurements of the temperature-and field-dependent magnetization, which increases dramatically up to ≈ 2.5 µB/f.u. as compared to the ordered compound (< 0.1 µB/f.u.). This study provides the first experimental realization of the metastable A2 structure in bulk Fe2VAl-based alloys and grants insight into the structure -property relationship of these materials. Our work confirms that temperature-induced antisite disorder, occuring during thermal heat treatment, can be a precisely tuneable parameter in the family of Heusler compounds.

Unexpected p-type thermoelectric transport arising from magnetic Mn substitution in Fe2V1−xMnxAl Heusler compounds

“…For Al-rich Fe 2 V 0.9 Mn 0.1 Al 1+y , the off-stoichiometry manifests itself through the presence of Al antisites on the Fe and V sites [69]. Overall, the crystallographic site occupancies can considerably affect the physical properties of Heusler compounds [70]. XRD patterns for Fe 2 V 0.9 Mn 0.1 Al 1+y sintered samples.…”

Giant Anomalous Hall and Nernst Conductivities in Magnetic All‐d Metal Heusler Alloys

“…The DFT‐based calculations are performed at zero Kelvin while in reality the synthesis conditions are usually under finite temperatures. Nevertheless, considering the high versatility of available synthesis techniques and processing parameters, [ 41 ] the DFT‐based predictions on the (meta‐)stable phases in this work can be regarded as good references to guide future experimental studies.…”