Study On The Prearation And Physical Properties Of Mn₂NiAl Alloys

People pay more attention on Heusler alloys with Hg₂CuTi structure since the Mn₂NiGawas discovered.The ferrimagnetic alloy may be likely to have a good development onapplications because its big recoverable strain , special change in magnetic properties andlarge magnetic-field-enhanced strain.At the same time,its martensitic transformationtemperature is close to room temperature.Recently, it was found that Mn₂NiAl alloy also hasthe Hg₂CuTi structure, and under room temperature may be likely to have a martensitetransition.In this thesis ,we studied on the preparation and physical properties of the Mn₂NiAlalloy.It was found that the material is highly ordered when the quenching temperature is at960℃or 970℃. Mn₂NiAl alloy which quenched from 960℃shows a strain of17000ppm at the temperature of 250K, and the strain is reversible at about 280 K.Furtermore, we also found that the higher order degree the lower magnetic transitiontemperature for Mn₂NiAl alloy.Theoretically, we calculated the electronic structures of Mn₂NiAl alloy with differenctlattice parameters. It was found that Mn₂NiAl alloy transformed from the metallicity intothe half-metallicity with the decreasing lattice. In addition, it should be noted that theMn₂NiAl alloys with half-metallicity dosen't follow the Slater-Pauling rules.We synthesized Mn-Ni-Cr-Al Heusler alloy with highly atomic ordering by thearc-melting method, it can be formed a single phase ,and in the low-angle we can see thesuperlattice peak.so Cr element greatly improved the phase of Mn₂NiAl alloy.At the sametime ,we studied the electronic structure and magnetic properties of Mn-Ni-Cr-Al alloys byfirst-principle.We analysed the DOS of Mn-Ni-Cr-Al alloys with different structures foundthat they to be ferrimagnetic ,half-metalllic, narrowband semiconductor.We also synthesized a series of Mn-Ni-Al alloys and Mn-Ni-Al alloys with Co, Fe elements adulteration. Studied the infection of Ratio of components to the alloys structure.we studied the structure, magnetic properties and martensite transition of Mn-Ni-Cr-Sballoys .Its martensite transition temperature is about 125K .Its reverse temperature is about170K, lag nearly 50K.Using first principles,we studied on CrMnNiZ (Z = Al,Ga,In,Si,Ge,Sn,Sb) series of alloys.We make sure the lattice of alloys by geometry optimization .The latticeparamenters mainly determined by atomic size.We aslo studied alloys'electronic structureand magnetic properties...