Research on new rare-earth half-metallic ferromagnets X0.75Eu0.25O (X=Ca, Sr and Ba) based on the first-principles calculations

• Half metallic ferromagnets (HMFs) are very important spintronic materials, which are the basis of so-called spintronic devices.
• Currently, corresponding studies focus mainly on d-type HMFs, d0f0-type HMFs, and HMFs containing rare-earth element La (no f-electrons) or Lu (being filled with 4f-electrons).
• However, there are few researches about rare-earth HMFs whose half-metallicity is from f-electrons, which have rich physical properties because of their special f-electron structures.
• Here the new rare-earth half-metallic ferromagnets X0.75Eu0.25O (X=Ca, Sr and Ba) with the NaCl structure all have high Curie temperatures and stable half-metallicity, and then they have great application potential for spintronics. Theoretic researches show that it is possible to prepare Sr0.75Eu0.25O and Ba0.75Eu0.25O experimentally.
• The supercell magnetic moments, the conductivity and the half-metallicity of X0.75Eu0.25O come mainly from the spin-polarization of Eu 4f-orbitals, which are caused by strong octahedral crystal field in the ligand compound ML6 consisting of the Eu-ion and six O-ions around it.

New rare-earth half-metallic ferromagnets X0.75Eu0.25O (X=Ca, Sr and Ba) with the NaCl structure are predicted based on the first-principles calculations. These materials only have up-spin subbands at the Fermi level and their net magnetic moments are all 7.00 µB per unit cell, which exhibits the evident half-metallic characteristics. Their energy gaps and half-metallic gaps are both wide so that they all have high Curie temperatures and stable half-metallicity, holding great potential applications in spintronics. From the calculated formation energies, it is possible to prepare Sr0.75Eu0.25O and Ba0.75Eu0.25O experimentally. However, it may be difficult to prepare Ca0.75Eu0.25O in experiments. The magnetic moments and the half-metallicity of X0.75Eu0.25O mainly originate from the spin-polarization of Eu 4f-orbitals, which are caused by the strong octahedral crystal field in the ligand compound ML6 consisting of the Eu-ion and six O-ions around it.

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