Oxides For Spintronics: A Review Of Engineered Materials For Spin Injection

Research on novel quantum phenomena of transition metal-doped ZrO2 nanosheets

The spintronic properties of cubic ZrO₂ (c-ZrO₂) nanosheets with intrinsic defects and transition metal (TM) elements doping have been systematically studied by first-principle calculation. The results show that impurity Fe has the lowest formation energy in each monolayer compared to other defects. The most stable (111) nanosheet, coupled with the higher defect formation energy, tends to disintegrate. Only Zr vacancy (V_Zr) on the (110) surface or O vacancy (V_O) on the (111) surface can generate a ferromagnetic ground state, while other intrinsic defects cannot introduce spin polarization. Ni-doped (110) monolayer cannot introduce a local magnetic moment, while Fe and Co can. The magnetic moments produced by Fe, Co, and Ni in the (111) sheet are 2, 4, and 1 µ_B, respectively. Further investigation revealed that the magnetism was mainly contributed by the d orbitals of the TM atom and the p orbitals of the surrounding O atoms. Magnetic couplings show that only Co-Co doped monolayers can produce macroscopic magnetism. These are predicted to produce T_Cs Curie temperature above room temperature when Co-Co distances are 5.070 and 6.209 Å on the (110) surface and 7.170 and 9.485 Å on the (111) surface. The research is beneficial to the refinement of the development of spintronics.

Understanding the role of 5d electrons in ferromagnetism and spin-based transport properties of K2W(Cl/Br)6 for spintronics and thermoelectric applications

The DFT calculation showed the half-metallic nature of K2WCl6 and K2WBr6 with their high Tc. Furthermore, the thermoelectric calculation showed that higher ZT values of K2WCl6 and K2WBr6 originated from ultra-low ke and high PF.

Systematic study of room-temperature ferromagnetism and the optical response of Zn1-x TM x S/Se (TM = Mn, Fe, Co, Ni) ferromagnets: first-principle approach

The structural, magnetic and optical characteristics of Zn_1-x TM _x S/Se (TM  =  Mn, Fe, Co, Ni and x  =  6.25%) have been investigated through the full-potential linearized augmented plane wave method within the framework of density functional theory. The optimized structures have been used to calculate the ferromagnetic and the antiferromagnetic ground-state energies. The stability of the ferromagnetic phase has been confirmed from the formation and the cohesive energies. The Heisenberg model is used to elucidate the Curie temperature (T _c) of these alloys. From the band structures and density of states plots, it has been observed that TM-doped ZnS/Se alloys appear to be semiconductors and exhibit ferromagnetism. In addition, the observed ferromagnetism has also been explained in terms of direct exchange energy Δ _x (d), exchange splitting energy Δ _x (pd), crystal-field energy (E _crys), exchange constants (N ₀ α and N ₀ β) and magnetic moments that shows potential spintronic applications. The optical behaviors of these alloys have been explained in terms of real and imaginary parts of the dielectric constant ε(ω), refractive index n(ω), extinction coefficient K(ω), reflectivity R(ω) and absorption coefficient σ(ω), in the energy range 0-25 eV. The calculated static limits of the band gaps and real part of the dielectric constants satisfy the Penn model. The critical limits of the imaginary part of the dielectric constants and absorption coefficients indicate that these alloys can be operated in the visible and the ultraviolet region of the electromagnetic spectrum; therefore, make them important for optoelectronic applications.

Oxygen vacancies controlled multiple magnetic phases in epitaxial single crystal Co0.5(Mg0.55Zn0.45)0.5O(1-v) thin films

High quality single-crystal fcc-Co_x(Mg_yZn_1-y)_1-xO_1-v epitaxial thin films with high Co concentration up to x = 0.5 have been fabricated by molecular beam epitaxy. Systematic magnetic property characterization and soft X-ray absorption spectroscopy analysis indicate that the coexistence of ferromagnetic regions, superparamagnetic clusters, and non-magnetic boundaries in the as-prepared Co_x(Mg_yZn_1-y)_1-xO_1-v films is a consequence of the intrinsic inhomogeneous distribution of oxygen vacancies. Furthermore, the relative strength of multiple phases could be modulated by controlling the oxygen partial pressure during sample preparation. Armed with both controllable magnetic properties and tunable band-gap, Co_x(Mg_yZn_1-y)_1-xO_1-v films may have promising applications in future spintronics.