Sputtered ferromagnetic europium oxide thin films for low temperature magneto-optic applications

Europium (II) oxide (EuO) is a promising material for low-temperature magneto-optic applications due to its ferromagnetic properties. EuO has a high magnetic moment of 7μB per Eu²⁺ ion, when below its Curie temperature of 69K. EuO rapidly oxidises to europium (III) oxide (Eu₂O₃) in standard atmospheric conditions making material growth challenging, typically requiring ultra-high vacuum molecular beam epitaxy or specialised evaporation setups.[1]

Here we demonstrate a reduction method to create ferromagnetic EuO films via sputtering Eu₂O₃ and capping with titanium. This shows potential in low-power optical modulation with the magneto-optic Faraday effect, rotating optical polarisation in the material when parallel or antiparallel to a magnetic field. The intensity of this is proportional to the Verdet constant of the material. Europium Chalcogenide materials have some of the highest recorded Verdet constants with a femtosecond-scale response rate, [2] making EuO an ideal material for rapid optical modulation. This has applications in the optical interfacing of low-temperature superconducting circuits.

[1] T. Mairoser et al., High-quality EuO thin films the easy way via topotactic transformation, Nat Commun 6, 1 (2015).

[2]F. Formisano, R. Medapalli, Y. Xiao, H. Ren, E. E. Fullerton, and A. V. Kimel, Femtosecond magneto-optics of EuO, Journal of Magnetism and Magnetic Materials 502, 166479 (2020).