Study On The Magnetic And Structural Properties Of Fe-Based And Mn-Based Heusler Alloys

In this thesis,Ni₅₀Fe₂₅Ga_25-xB_x(x=0-4)alloys were prepared by arc-melting. ThenXRD, and AC susceptibility were used to test the ma gnetic properties, structure andphase-transformation of these alloys The melt-spun ribbons were prepared by a singlewheel technique with the substrate velocity (Vs) of 25m/s. The study of theNi50Fe₂5Ga25-x Bx(x=0-4)show that the lattice consta nt decreased with increased of B,this ma inly come from the sma ller atomic radius of B compared with that of Ga.Meanwhile we discover that the Curie temperature phase transformation temperatureshow a decreasing trend with increasing B content.based on the first-principle s calculation we studied the electron structure,ma gnetic properties and phase stability of the Heusler alloys Ni₂FeZ(Z=B,Al,Ga,In)with the GGA and LDA approxima tions. We calculated the electronic structures ofthese compounds with different BCC and FCC structures in ferroma gnetic state. Theresults indica te that the lattice consta nt of the Ni₂FeZ(Z=B,Al,Ga,In)alloysincreased with the Z changing from B to In . The increasing of the lattice is due to theatomic radius of the Z atom,and the alloys are ferroma gnetic materia l with strongma gnetic. Different Z atoms have influence on the phase stability of these compounds.A series of Fe_1.5M_0.5CoSi (M = V, Cr, Mn, Fe) alloys have been synthesizedsuccessfully. The effect of low-va lent atoms on the electronic structure and ma gneticproperties of Fe₂CoSi has been studied theoretica lly and experimentally. Theoreticalcalculations suggest that the M atom prefers substituting for Fe at the B site ratherthan entering the (A, C) sites. It is found that doping of low-va lent atoms helps to openthe minority gap around EF and pushes the majority spin states high on energy scale,which leads to a high spin polariza tion in these alloys. The substitution for Fe does notdecrease the Curie temperature too much. The TC of them is all higher than 650K. Thecalculated total spin moments agree with the experimental va lue well and decrease with decreasing number of valence electrons of the M atom, following the Slater-Pauling curve.In the same way, we calculate the energy-la ttice consta nt curves of the Fe₂YB(Y=Cr,Mn, Co) alloys and analyse the electron structure and figure out the spinpolariza tion ratio. The results of calculation show that they have a high spinpolariza tion ratio.