The Study Of Magnetic And Transport Properties On Ni-Based Heusler Alloys

Heusler alloys are ternary intermetallic compounds with stoichiometric composition X₂YZ. Heusler alloys have stimulated much research interest since the discovery of a large magnetic shape memory effect in Heusler compounds Ni₂MnGa.Our specimens were synthesized by melt spinning method. In this thesis, the primary content is the study on the magnetic and transport properties of the Heusler alloys Ni₅₃Mn₂₅Al₂₂, Ni₅₅Mn₂₀Al₂₅ and Ni₂CoAl. X-ray diffraction (XRD) spectra were performed to identify the structure on the polycrystalline samples. The magnetizations were measured using both a physical property measurement system (Quantum Design PPMS, USA) and a superconducting quantum interference device (SQUID). The resistance measurements were carried out by means of a standard ac four-point technique at temperatures ranging from 5 to 350K employing the physical property measurement system (Quantum Design PPMS, USA). The transformation temperatures were determined by differential scanning calorimetry (DSC) at a rate of 10 K/min.We can see that the Ni₅₃Mn₂₅Al₂₂ ribbon having a B2 structure exhibits that a magnetic transition from antiferromagnetic to paramagnetic and a structural transition of austenitic-martensitic character which has a high Ms of 278K coexist. The calculated effective paramagnetic moment of 4.47μB per formula unit reveals Mn atoms contribute to the paramagnetism of the B2 phase in this alloy.Ni₅₅Mn₂₀Al₂₅ also have a B2 structure, from the measurement of resistance we can find a decreas near room temperature, that means there are some transformation have taken place, and the transition temperatures are determined. The effect of the applied field on the resistance at different temperatures is also discussed.In the study of Ni₂CoAl, it exhibits tetragonal structure at room temperature,...