Elaboration of the magnetically frustrated GeFe2O4 spinel thin films by pulsed laser deposition

Magnetic frustration is a key research focus in condensed matter physics, where competing spin-spin interactions give rise to emergent phenomena that challenge conventional understanding and lead to topological effects with potential applications in quantum technologies. The direct spinel GeFe 2 O 4 has recently garnered renewed interest for the plethora of magnetic behaviours it is able to demonstrate. Here, we report on the pioneering stabilization of GeFe 2 O 4 thin films via pulsed laser deposition on MgO (001) substrates. The ablation procedure has been optimized to counterbalance the large volatility of the Ge species compared to the Fe ones, granting a fine control over the compositional homogeneity and stoichiometry of the films. Atomic force microscopy measurements rendered thin film surfaces with very low roughness values in the range of 0.2 nm, and X-ray diffraction data confirmed the epitaxial growth of the films and their high crystallinity with no detectable presence of spurious phases. SQUID magnetometry measurements revealed the expected antiferromagnetic behaviour, albeit with ordering temperatures higher than the expected bulk value. This discrepancy could be explained accounting for a small deviation from the direct spinel structure, as unveiled by resonant elastic X-ray scattering measurements, and from the resulting partial occupation of the tetrahedral sites by Fe atoms. Finally, varying the laser fluence we could tune the Fe/Ge ratio and provide a control over the ordering temperature from a modification of the spin-spin super-exchange network paths. Our results pave the way to further studies to explore emergent magnetic properties in GeFe 2 O 4 -based heterostructures. • Optimization of the PLD procedure used to obtain stoichiometric GeFe 2 O 4 films. • First obtention of low roughness, well-crystallised, epitaxial GeFe 2 O 4 thin films. • Possibility to tune the magnetic order temperature by changing the Fe/Ge ratio.