Scanning tunneling microscopy study of Ni2MnGa(100) surface

TL;DR

This study uses scanning tunneling microscopy to explore the surface structures of Ni2MnGa(100) in different phases, revealing novel coexistence of twined morphology and charge density waves, and their dependence on composition and phase.

Contribution

It reports the first observation of coexistence of twined morphology and incommensurate charge density waves in the premartensite phase of Ni2MnGa(100).

Findings

Coexistence of twined morphology and CDW in premartensite phase.

Transformation of incommensurate to commensurate CDW in martensite phase.

Voltage-dependent STM and STS confirm morphology-CDW relationship.

Abstract

Ni2MnGa(100) surface has been investigated in the premartensite and martensite phase by using scanning tunneling microscopy. The presence of twined morphology is observed in the premartensite phase for Mn excess surface which exhibit non-equispaced parallel bands in one side of the twin boundary. Moreover, in the flat region of the surface two domains of non-periodic parallel bands corresponding to the incommensurate CDW is observed. Although, stoichiometric surface also exhibit twining but the parallel bands are equispaced and have equal corrugation. Most interestingly, coexistence of twined morphology and the CDW pattern is observed in the premartensite phase for Ni excess surface which was not reported till date. In the martensite phase for Mn excess surface, incommensurate CDW is transformed to commensurate CDW corresponding to the equispaced parallel bands. In stark contrast, stoichiometric surface exhibit parallel bands that have different periodicity in different regions. Both the voltage dependent STM and STS measurement establishes that this morphology is also related to the CDW.