Room temperature spin filtering in epitaxial cobalt-ferrite tunnel barriers

Abstract

We report direct experimental evidence of room temperature spin filtering in magnetic tunnel junctions (MTJs) containing CoFe2O4 tunnel barriers via tunneling magnetoresistance (TMR) measurements. Pt(111)/CoFe2O4(111)/γ-Al2O3(111)/Co(0001) fully epitaxial MTJs were grown in order to obtain a high quality system, capable of functioning at room temperature. Spin polarized transport measurements reveal significant TMR values of -18% at 2 K and -3% at 290 K. In addition, the TMR ratio follows a unique bias voltage dependence that has been theoretically predicted to be the signature of spin filtering in MTJs containing magnetic barriers. CoFe2O4 tunnel barriers therefore provide a model system to investigate spin filtering in a wide range of temperatures.

Effect of epitaxial strain on the cation distribution in spinel ferrites CoFe2O4 and NiFe2O4: A density functional theory study

“…This preference for the inverse spinel structure is reduced by tensile epitaxial strain, which can lead to strong sensitivity of the cation distribution on specific growth conditions in thin films. Furthermore, we obtain significant energy differences between different cation arrangements with the same degree of inversion, providing further evidence for recently proposed short range B site order in [3][4][5][6][7] These applications require the growth of high quality thin films of CFO and NFO on suitable substrates. However, the electronic and magnetic properties of the corresponding films can depend strongly on substrate, film thickness, and specific preparation conditions, and eventually differ drastically from the corresponding bulk materials.…”

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

“…As the Curie temperature of ferrites is well above room temperature, efficient roomtemperature spin-polarized sources could be obtained using these oxides. However, room-temperature spin filtering has only been reported in CoFe 2 O 4 -based tunnel junctions 8,10 due to the difficulty of fabricating room-temperature ferrimagnetic barriers.…”

The magnetization of epitaxial nanometric CoFe2O4(001) layers

“…In recent years, ͑ferri͒magnetic spinel insulating oxides, such as NiFe 2 O 4 or CoFe 2 O 4 ͑CFO͒, have received much attention due to their potential use in advanced spintronic devices such as spin filters 1-5 or in multiferroic actuators. 6 Some of these applications require growth of epitaxial layers of these materials on suitable substrates, with sharp interfaces with substrates and bottom or upper layers.…”