Epitaxial growth and ferrimagnetic behavior of MnFe2O4(111) ultrathin layers for room-temperature spin filtering

We report on the epitaxial growth and physical properties of spinel MnFe2O4(111) thin films with thicknesses down to 2 nm. The thin films, grown on alpha-Al2O3(0001) single crystals or Pt(111) buffer layers by oxygen-assisted molecular beam epitaxy, exhibit high structural order with sharp interfaces and low roughness. The electrical and magnetic properties are carefully investigated and it is shown that MnFe2O4(111) ultrathin films keep an insulating and ferrimagnetic behavior at room temperature. Special attention is given to the iron/manganese valence state and the cationic ordering. X-ray absorption spectroscopy and magnetic circular dichroism measurements reveal that thin films contain mainly Fe3+ and Mn2+ cations, distributed predominantly in a normal spinel structure. This study proves the high potential of MnFe2O4 to be used as a magnetic tunnel barrier for spin filtering applications at room temperature.