Lattice dynamics effects on magnetocrystalline anisotropy energy of YCo₅ from first principles

YCo₅ has attracted much attention due to its large magnetocrystalline anisotropy (MCA) energy, which decays as the temperature increases. So far, the origin of the temperature decay has been attributed solely to the spin fluctuation [1]. At elevated temperatures, however, the thermal excitation of phonons is expected to influence the MCA energy significantly, as in the case of MnBi [2].

In this study, we investigated lattice dynamics (LD) effects on the MCA energy of YCo₅ using first-principles calculations. We show that YCo₅ is dynamically unstable within harmonic approximation, and this instability can be stabilized either by reducing the number of valance electrons or increasing temperature. We calculated the temperature-dependent MCA energy using both LD and ab initio molecular dynamics (AIMD) methods. We show that the MCA energies determined using both approaches decrease significantly with temperature. We discuss the origin of this temperature decay based on these approaches.

[1] C. E. Patrick et al. Phys. Rev. Lett. 120, 097202 (2018)

[2] A. Uruu et al. Phys. Rev. B 102, 115126 (2020)