CrO2-based heterostructure and magnetic tunnel junction: perfect spin filtering effect, spin diode effect and high tunnel magnetoresistance

Half-metallic ferromagnetic CrO₂ has attracted much interest due to its 100% spin polarization and high Curie temperature. CrO₂ films have been fabricated on a TiO₂ (100) substrate. However, there have been no reports on the spin transport properties of devices based on a CrO₂ electrode and TiO₂ barrier. In this work, we use first-principles calculations combined with a nonequilibrium Green's function method to investigate the bias-voltage-dependent spin transport properties for the CrO₂/TiO₂ (100) heterostructure and the CrO₂/TiO₂/CrO₂ (100) magnetic tunnel junction (MTJ). Our results reveal the excellent spin filtering effect and spin diode effect in the heterostructure as well as the high tunnel magnetoresistance ratio (up to 4.48 × 10¹⁴%) in the MTJ, which indicate potential spintronic applications. The origins of these perfect spin transport characteristics are discussed in terms of the calculated spin-dependent electrode band structures, the spin-dependent transmission spectra and semiconductor theory.

Spin-dependent device density of states in the CrO₂/TiO₂/CrO₂ magnetic tunnel junction.

Tuning the magnetic properties of graphene derivatives by functional group selection

The recent discovery of hydroxofluorographene G(OH)F, a graphene derivative showing room temperature antiferromagnetic ordering, suggests that there may be other sp-materials based on sp³-functionalized graphene that exhibit magnetic ordering and whose properties can be controlled by selecting suitable functional groups.

Phagraphene nanoribbons: half-metallicity and magnetic phase transition by functional groups and electric field

Magnetic nanomaterials with the desirable nature are the basis for developing future spintronic devices, and research for them is of fundamental interest. Here, we explore the realization of half-metallicity and magnetic phase transition for phagraphene nanoribbons in virtue of functional groups (OH and CN) with different coverage fractions and external electric fields. The first-principles calculations show that a single-edge CN functionalization only makes a intrinsic spin-degenerate semiconducting ribbon converted to a quasi-metal or metal, while a single-edge OH modification leads to an occurrence of the half-semiconducting nature regardless of the coverage fraction of groups. Interestingly, the half-metal behavior for the CN and OH double-edge modified ribbons can be achieved either in the zero-electric-field intrinsic state for most of functionalized systems or at a very low electric field, 0.1 V Å^-1. More importantly, the observed critical electric field for the transition from ferromagnetic to nonmagnetic phase is lowered significantly almost for all systems, this benefits to design a low electric-field-controlling magnetic switch which can reversibly work between both magnetic and nonmagnetic states. The calculated Gibbs free energy confirms that the group-modified ribbons generally hold a more favorable energy stability in most of the cases, facilitating likely experimental realization.