Phase transitions in Ni2+xMn1-xGa with a high Ni excess

Abstract

Ferromagnetic shape memory alloys Ni${}_{2+x}$Mn${}_{1-x}$Ga were studied in the range of compositions $0.16\le x\le 0.36$. Experimental phase diagram, constructed from differential scanning calorimetry, transport and magnetic measurements, exhibits distinctive feature in a compositional interval $0.18\le x\le 0.27$, where martensitic and magnetic transitions merge in a first-order magnetostructural phase transition ferromagnetic martensite $\leftrightarrow$ paramagnetic austenite. Observed in this interval of compositions a non-monotonous behavior of the magnetostructural phase transition temperature was ascribed to the difference in the exchange interactions of martensitic and austenitic phase and to the competition between increasing number of valence electron and progressive dilution of the magnetic subsystem which occur in the presence of a strong magnetoelastic interaction. Based on the experimental phase diagram, the difference between Curie temperature of martensite $T_C^M$ and Curie temperature of austenite $T_C^A$ was estimated. Influence of volume magnetostriction was considered in theoretical modeling in order to account for the existence of the magnetostructural phase transition over a wide range of compositions.

11 pages, 6 figures, misprint corrected

References in corpus (7)

• Shape memory ferromagnets
• Coexistence of ferro- and antiferromagnetic order in Mn-doped Ni${}_2$MnGa
• Giant entropy change at the co-occurrence of structural and magnetic transitions in the Ni2.19Mn0.81Ga Heusler alloy
• Magnetic properties and magnetostructural phase transitions in Ni2+xMn1-xGa shape memory alloys
• Magnetic properties of Ni2.18Mn0.82Ga Heusler alloys with a coupled magnetostructural transition
• Magnetocaloric effect and magnetization in a Ni-Mn-Ga Heusler alloy in the vicinity of magnetostructural transition
• The magnetic field influence on magnetostructural phase transition in Ni2.19Mn0.81Ga

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• Temperature dependence of the anomalous Nernst effect in Ni${}_2$MnGa shape memory alloy
• Ferromagnetic interactions and martensitic transformation in Fe doped Ni-Mn-In shape memory alloys
• Electronic structure beyond the generalized gradient approximation for Ni${}_2$MnGa
• Strain and order-parameter coupling in Ni-Mn-Ga Heusler alloys from resonant ultrasound spectroscopy
• Effect of site occupancy disorder on Martensitic properties of Mn${}_2$NiIn type alloys: x-ray absorption fine structure study
• Composition and temperature dependence of the thermoelectric power of Ni${}_{2+x}$Mn${}_{1-x}$Ga alloys