Exploring the structural stability and related physical properties of FePt2 alloys

Abstract

The current work presents a theoretical study of the physical properties of several FePt2 ordered structures through first-principles calculations, including structural, magnetic, electronic, mechanical, phonon and thermal properties. The structural stabilities are certified by the enthalpies of formation, elastic constants, and phonon dispersion relationships. The tetragonal I4/mmm structure is energetically favorable compared to other types FePt2 structures including Cmcm, Immm, P63/mmc and P4/nmm structures. The electronic density of states and the contributions of each d-orbital electron to the magnetic moment are analyzed to understand their magnetism. The bulk modulus B values of these FePt2 structures are similar, but the Young's modulus E and shear modulus G as well as the elastic anisotropy are quite different. The thermal properties at finite temperature are estimated by the quasi-harmonic approximation. The I4/mmm structure has higher isothermal bulk modulus, lower thermal expansion coefficient and weaker thermal expansion anisotropy, which is more suitable for high temperature applications than other structures. Also, the sequence of thermal expansion anisotropy is P4/nmm > Immm > Cmcm > I4/mmm (≈P63/mmc).