Ab initio study of electronic temperature effects on magnetic materials properties

We present ab initio calculations of the electronic temperature dependence of the magnetization, electronic energy, and specific heat of FePt ${L1}_{\text{0}}$, fcc-Ni, hcp-Co, and bcc-Fe. We find that atomic magnetic moments in each compound disappear at very high temperature, ranging from 3100 to 8100 K. However, for some compounds, the consequences of this phenomenon are noticeable on the electronic energy and specific heat even at low electronic temperature. Consequently, large deviations from the Sommerfeld approximation and from some previous work that did not take into account explicitly the dependence of the electronic structure on the electronic temperature are shown. Our results are of interest in the field of laser-induced ultrafast magnetization dynamics, since they provide a more precise estimate of the electronic specific heat that enters in the three-temperature model.

Figure 1

Spin-polarized density of states of fcc-Ni, hcp-Co, bcc-Fe, and FePt ${L1}_{\text{0}}$ for different values of the electronic temperature chosen below and above the Stoner temperature. The majority- (minority-) spin DOSs are in orange (blue), and the value of $\mu$, the chemical potential, is indicated by a vertical dashed line.

Figure 2

Magnetic moment per unit cell against the electronic temperature. In every compound, we observe a loss of magnetization when the temperature is above $T_S$.

Figure 3

Electronic energy per unit cell against the electronic temperature for fcc-Ni, hcp-Co, bcc-Fe, and FePt ${L1}_{\text{0}}$. The electronic energy obtained from TDD (TID) calculations is in blue (orange).

Figure 4

Electronic specific heat vs the electronic temperature for fcc-Ni, hcp-Co, bcc-Fe, and FePt ${L1}_{\text{0}}$ computed with different approximations.