Computer Simulation Studies Of The Structure Transition And High-pressure Physical Properties For Mn₂RuZ?Z=Si,Ge,Sn? Heusler Alloys

Heusler alloys are a hot topic in new metal functional materials due to their rich physical properties and so many applicable functions.The emerging Mn-based full heusler alloys containing 4d or 5d elements in recent years expanded the research scope of this materials.In this paper,the first-principles calculation method based on the density function theory and the quasi-harmonic Debye model have been carried out to investigate the electronic,magnetic,elastic and thermodynamic properties of three new synthesized heusler alloys Mn₂RuZ Si,Mn₂RuZGe and Mn₂RuZ Sn from the atomic scale.The target of this paper is to revel the structure properties of these three alloys in ordinary conditions and also provide a reliable basis for their material behavior under critical conditions.The main work contains the following sections.Firstly,according to the characteristic of research objects and methods,we selected suitable calculation parameters to investigate the electronic,magnetic and phase transition properties of Hg2 Cu Ti-type Mn₂RuZ Z?Z=Si,Ge,Sn?alloys in details.The relationship between the convergence of calculations and the key parameters demonstrated that the calculation results reliable.Through the comparison,we found they are all ferrimagnetic,and the magnetic moment are mainly determined by the antiparallel aligned Mn element.The Mn₂RuZ Si and Mn₂RuZGe alloys behaved as half-metallic materials and this property will be maintained in a certain lattice range.We also predict the possibility of the phase transformation for Mn₂RuZ Sn alloy in a given volume,and the small energy difference and large magnetic transformation between cubic and tetragonal structure indicate its great potential to be used as a new type of magnetic shape memory alloy.Then,we presented a detailed investigation on the elastic properties of Hg₂CuTi-type Mn₂RuZ?Z=Si,Ge,Sn?alloys under high pressures.We set the strain of the optimized equilibrium cells to a finite value by applying a given homogeneous deformation to optimize the internal atomic coordinates and calculate the resulting stress;each of the second-order elastic constants of the single crystals was determined by means of a least-squares linear fit of stress against strain.It is found that these three alloys show bettermechanical stabilities under different pressures where the Mn₂RuZ Si is stable in the pressure range of 0-100 GPa,the Mn₂RuZGe is stable in the pressure range of 0-50 GPa and the Mn₂RuZ Sn is stable in the pressure range of 0-30 GPa.Accroding to the elastic constants,the change principles of the bulk modulus,shear modulus,Young's modulus,Poisson's ratio,lattice wave velocity and Debye temperature along with different pressures have been calculated.Finally,combined with the quasi-harmonic Debye model,we use the first-principles calculations which based on the density function theory to investigate the thermodynamic properties of Hg2 Cu Ti-type Mn₂RuZ Si up to100 GPa,Mn₂RuZGe up to 50 GPa,and Mn₂RuZ Sn up to 30 GPa respectively.Based on the discussion of the thermodynamic properties,such as bulk modulus,thermal expansion coefficient,heat capacities,entropy,Debye temperature,and Grüneisen parameter,the important conclusions are obtained for the Mn₂RuZ Si in the temperature range of 0-1200 K and the Mn₂RuZGe and Mn₂RuZ Sn alloys in the temperature range of 0-900 K.