Experimental Study And First-Principles Study Of Co Doping Ni₅₀Mn₃₉Sn₁₁ Alloy

A series of Ni_50-xCo_xMn₃₉Sn₁₁（x=0-8）alloy ribbons were prepared by a single-roll melt spinning method and its crystal structure,phase transition,magnetocaloric,and magnetoresistance effect are investigated.Using the software of Materials Study,the first principles calculation method is used to study the reasons for the improvement of austenite phase structure stability and magnetic properties after Co substitution for Ni atoms.Through together the experimental and first-principle calculation results,the doping effect of the Co element in the alloy is discussed.The specific contents are as follows:（1）It was found that the MT temperature decrease progressively and the Curie temperature continuously increase with the increase of Co content,the magnetic properties of Austenite phase is Enhanced at the same time.A larger magnetic entropy change is found in x=5,6,7 alloy near room temperature.The composition effect of the Co element is explained preliminarily by using the theory of valence electron concentration（e/a）and austenite lattice structure.（2）By scanning the Microstructure of cross-section perpendicular to the ribbon plane and measuring magnetic in different directions,it is found that the structure of Ni_50-xCo_xMn₃₉Sn₁₁1 ribbon has obvious directionality.（3）Magnetoresistance characteristics of Ni_50-xCo_xMn₃₉Sn₁₁（x=5-8）alloy ribbons during phase transformation were measured.In the phase transition region,the peculiar electrical transport properties of materials were found under the induce of variable magnetic field.The magnetoresistance characteristics in Ni₄₂Co₈Mn₃₉Sn₁₁1 reached 25%at 30 kOe and 270 K.The mechanism of resistance variation induced by magnetic field is explained preliminarily.（4）The effect of Co addition on the state density and lattice parameters for Ni-Mn-Sn alloy was studied by the first principle.The result shows that:the addition of Co changes the distribution of the density of spin downwards at the fermi energy level,forming a pseudo energy gap which is beneficial to the stability of the structure.It has little effect on the density of spin upwards of Ni-Co-Mn-Sn parent phase.More Co3d-Mn3d hybridization replaced Ni3d-Mn3d hybrids was found with the increase of Co substitution for Ni.With the content of Co increases,the cell volume reduces continuously.These factors make the parent phase of the alloy more stable,which is the basic reason for the martensitic transformation temperature decreasing,the Curie temperature rising,magnetocaloric effect and magnetoresistance effect increasing.Calculation and experimental results is interpreted.