Transparent EuTiO3 films: a possible two-dimensional magneto-optical device

Abstract

The magneto-optical activity of high quality transparent thin films of insulating EuTiO3 (ETO) deposited on a thin SrTiO3 (STO) substrate, both being non-magnetic materials, are demonstrated to be a versatile tool for light modulation. The operating temperature is close to room temperature and allows for multiple device engineering. By using small magnetic fields birefringence of the samples can be switched off and on. Similarly, rotation of the sample in the field can modify its birefringence Δn. In addition, Δn can be increased by a factor of 4 in very modest fields with simultaneously enhancing the operating temperature by almost 100 K.

Intriguing spin–lattice interactions in EuTiO3

“…The origin of this enhancement stems from strong spin–lattice coupling which on the one hand modifies the lattice dynamics, on the other hand the spin activity 7 , 15 . The interplay between both was predicted to induce “hidden” spin order visible in the magnetic susceptibility 16 , the birefringence 17 , the Raman response 18 , the lattice constants 19 and the dielectric properties 20 . Very convincing breakthrough confirmations of these predictions have been achieved by muon spin rotation (µSR) experiments 21 – 24 , which are the most sensitive tools to detect any kind of magnetic order, even if this is not visible by bulk probing experiments.…”

Magnetic interactions and the puzzling absence of any Raman mode in EuTiO3

“…An intrinsic magnetism was predicted even in the paramagnetic phase, due to strong spin lattice coupling since the second nearest neighbor exchange constant directly depends on the spin–lattice coupling constant. [ 12,32 ] This effect is intimately related with the findings from birefringence, EPR, and muon spin rotation (μSR) experiments where a small magnetic field activated birefringence in a EuTiO 3 thin film [ 34 ] and magnetic activity was detected. [ 12 ]…”

“…Possibly, the increase at ~200 K (with or without an external magnetic field) and at ~70 K (with the field) are related with those observed in Guguchia et al [ 12 ] of muon scattering measurements and in the birefringence of ETO epitaxial film. [ 34 ]…”

“…Birefringence data clearly support that a magnetic field of the same order of magnitude as the magnetic fields used here affects the structural phase transition temperature. [ 34 ]…”

Defect engineering of magnetic ground state in EuTiO3 epitaxial thin films

“…Perovskite EuTiO 3 (ETO) is a promising candidate for studying defect‐related physics because the energy scales of the lattice, charge, and spin degrees of freedom are similar and can hence be tuned by multiple parameters such as epitaxial strain, isotropic pressure, chemical doping, and electric field 19‐40 . Bulk ETO is a G‐type AFM with a spin moment of J = S = 7/2 on each Eu site 19,20 .…”