Search

Spin polarization and magnetic anisotropy are key properties that determine the performance of magnetic tunnel junctions (MTJs), which are utilized in various spintronic devices. Although materials that have both high spin polarization and sufficient perpendicular magnetic anisotropy are desirable for further developments of MTJs, such materials are rare because electronic structures necessary for achieving these two properties are distinct. Here, we experimentally show the inverse spinel ferrimagnet NiCo2O4 (NCO), whose band structure is theoretically predicted to be half-metallic, has both high spin polarization and perpendicular magnetic anisotropy. Perpendicular MTJs with NCO magnetic electrodes exhibit magnetoresistance up to 230%, indicating that the spin polarization of perpendicularly magnetized NCO is as high as −73%. Our experimental results demonstrate the potential of NCO as a half-metal with perpendicular magnetic anisotropy, which will lead to new paradigms for designing and developing all-oxide spintronic devices.

The temperature performance of metal–oxide–silicon tunneling light-emitting diodes was studied. An electron–hole-plasma model can be used to fit all the emission spectra from room temperature to 98 K. At constant voltage bias in the accumulation region, the normalized integral emission intensity slightly increases at low temperature with activation energy as low as 12 meV. From room temperature down to 98 K, the extracted band gaps are ∼80 meV lower than the value of Varshni equation, and the linewidth drops from 65 to 30 meV. The transverse optical and longitudinal optical phonons are involved in the light-emission process due to the reduction of extracted band gaps and the resemblance between electroluminescence and photoluminescence spectra at similar temperature.

An electron-hole plasma recombination model is used to fit the room-temperature electroluminescence from metal–oxide–silicon tunneling diodes. The relatively narrow line shape in the emission spectra can be understood by the quasi-Fermi level positions of electrons and holes, which both lie in the band gap. This model also gives a narrower band gap than that of bulk silicon. The surface band bending in the Si/oxide interface is responsible for this energy gap reduction.