The optical reflectivity of single crystals of ${\mathrm{Eu}}_3$${\mathrm{O}}_4$ has been investigated in the photon energy range between 0.03 and 12 eV. The dielectric functions have been derived by means of a Kramers-Kronig analysis and interpreted with lattice vibrations and interband transitions from initial ${\mathrm{Eu}}^{2+}$, ${\mathrm{Eu}}^{3+}$, and $2p^6$ states into crystal-field-split $5d$ bands. In addition intra $4f^6$ transitions have been observed and commented on. The Coulomb correlation energy between ${\mathrm{Eu}}^{2+}$ and ${\mathrm{Eu}}^{3+}$ has been found experimentally. Optical transmission measurements at low temperatures have revealed a blue shift of the absorption edge for temperatures above the Néel point $T_N$ and in zero external magnetic fields and a red shift of the absorption edge for magnetic fields larger than a critical field $H_c=2.4\mathrm{}$ kOe, confirming the metamagnetic phase. $T_N$ is found to be 5.2±0.2 K.

• Received 23 June 1975

DOI:https://doi.org/10.1103/PhysRevB.12.3940