Abstract
An experimental study has been performed on a series of Ni2Mn0.4-xFexCr0.6Ga Heusler alloys. At room temperature, the alloys crystallize in either the tetragonal martensite (x < 0.1) or cubic L21 structure (x ≥ 0.1). Additionally, a Cr-Fe based face-centered cubic γ-Fe type secondary phase was found to co-exist in the samples. Magnetization and transport measurements revealed that the Curie and martensitic transition temperatures decrease as Mn is replaced with Fe. Atypical to other Ni2MnGa-derivative Heusler alloys, the transition temperatures decrease at the same rate with respect to x for x ≥ 0.1. Thus, the two transitions do not couple in to a single magnetostructural transition at any composition. Transport measurements revealed that all samples exhibit a sharp drop in resistivity during the martensitic phase transition (13 - 17 %), with the magnitude of this drop remaining relatively constant over the entire series. The possible origins of the observed experimental behavior are discussed.
Highlights
Materials that exhibit magnetic and structural transitions are of significant interest due to the fact that they are often accompanied by exciting phenomena, such as giant magnetocaloric effects,[1] large magnetoresistance,[2] ferromagnetic shape memory effects,[3] and exchange bias effects.[4]
We present an experimental study on a system of Ni2Mn0.4-xFexCr0.6Ga Heusler alloys
For x < 0.10, the alloys were found to crystallize in the tetragonal martensite structure while the alloys with x ≥ 0.10 primarily exhibited the cubic L21 structure
Summary
Materials that exhibit magnetic and structural transitions are of significant interest due to the fact that they are often accompanied by exciting phenomena, such as giant magnetocaloric effects,[1] large magnetoresistance,[2] ferromagnetic shape memory effects,[3] and exchange bias effects.[4] In recent years, Ni2MnGa-derivative Heusler alloys have been a topic of intense research interest, given that they often exhibit the coupled first order magnetic and martensitic phase transition (MPT) which intensifies the aforementioned phenomena.[5] The MPT is a non-diffuse structural transition from a high temperature cubic phase (austenite) to a low-symmetry phase (orthorhombic, tetragonal, or monoclinic martensite) at low temperatures.[6,7] The physical origin of the MPT in Heusler alloys has been attributed to the valence electron concentration (e/a), interatomic spacing, and the development of hybrid states between Ga p and Ni d electronic orbitals Ferromagnetism in these materials is believed to arise from indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions between neighboring Mn atoms, mediated by the conduction band electrons.[8] Consequentially, the Curie temperature, the martensite transition temperature, and the structure of the martensite phase are heavily dependent on the elemental composition. The motivation was to build on the work of the Ni2Mn1-xCrxGa series by investigating how T C and T M change as Mn is replaced with Fe, and to explore the nature of the change in resistivity at T M
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