High-pressure tuning of valence and magnetic interactions in Eu${}_{0.5}$Yb${}_{0.5}$Ga${}_4$

Pressure-induced changes in valence and magnetic ordering are observed in a Eu${}_{0.5}$Yb${}_{0.5}$Ga${}_4$ compound by means of element selective x-ray absorption spectroscopy at Eu and Yb $L_3$ edges. Concomitant Eu and Yb valence transitions towards a $3+$ state, together with an antiferromagnetic to ferromagnetic transition, are observed with applied pressures up to 30 GPa. With the support of density functional theory calculations, we argue that hybridization between (Eu/Yb)-5$d$ and Ga orbitals regulates the valence and magnetic exchange interactions in this system.

Figure 1

X-ray diffractogram of a powdered Eu${}_{0.5}$Yb${}_{0.5}$Ga${}_4$ single crystal at 300 K and ambient pressure.

Figure 2

Magnetization of Eu${}_{0.5}$Yb${}_{0.5}$Ga${}_4$ vs temperature (upper panel) and magnetic field (lower panel). We also show the results for EuGa${}_4$ and YbGa${}_4$ for comparison.

Figure 3

Europium $L_3$ XANES and XMCD spectra obtained at $T=6$ K and ${\mu }_{0}H=4$ T for a powdered sample as a function of applied pressure. The characteristic XANES peaks of Eu${}^{2+}$ and Eu${}^{3+}$ are identified. (r) indicates measurement done after pressure release. Inset: XMCD peak amplitude as a function of applied pressure.

Figure 4

Europium $L_3$-edge XMCD peak amplitude obtained at 4 T for ambient pressure and 4 GPa as a function of the temperature. For a comparison we also plotted the magnetization obtained in a SQUID magnetometer and all the curves were normalized at lowest temperature.

Figure 5

Hysteresis curves of the Eu $L_3$ XMCD peak amplitude as a function of applied pressure. For comparison we show the magnetization at ambient pressure obtained in a SQUID magnetometer. Inset: Coercive vs pressure. All data were taken at $T=6$ K.

Figure 6

(a) Calculated density of states for Eu $5d,4f$ orbitals and Ga total DOS showing electronic hybridization between Eu-5$d$ and Ga orbitals. (b) Electronic occupation numbers for Eu-5$d$ and Ga-3$d$ as a function of lattice contraction. The simulations were done on the parent compound EuGa${}_4$.

Figure 7

Ga $K$-edge XANES and XMCD spectra of Eu${}_{0.5}$Yb${}_{0.5}$Ga${}_4$ measured at a temperature ($T$) of 3 K and 4 T magnetic field. XMCD is plotted for both field directions $(\pm 4$ T) to account for artifact effects in the polarization-switching mode. The XMCD signal is evidenced by the sign switching of the spectra measured with +4 and $-4$ T applied magnetic field.

Figure 8

Ytterbium $L_3$-edge XANES and XMCD spectra measured at $T=6$ K, 4 T applied magnetic field, and as a function of applied pressure. Yb${}^{2+}$ and Yb${}^{3+}$ characteristic XANES peaks are identified.