Spin-up Carriers Research Articles

Effect of a flat band on a multiband two-dimensional Lieb lattice with intra- and interband interactions

In this study, we explore the effect of a single flat band in the electronic properties of a ferromagnetic two-dimensional Lieb lattice using the multiband Hubbard model with polarized carriers, spin-up and spin-down. We employ the self-consistent dynamical mean field theory and a Green functions cumulant expansion around the atomic limit to obtain the correlated densities of states while varying the intra- and interband interactions. Our findings demonstrate a renormalization of the correlated density of states in both the spin-up and spin-down carriers as we varied the intra- and interband interactions. We conclude that the presence of a flat band enables the system to maintain a metal state with itinerant ferromagnetism in the spin-up carrier.

Tunable magnetization and spin transfer induced by electric field in magnetic ultrathin BiFeO3 layer

First-principles density-functional theory calculations show that switching of magnetization by 90° can be achieved in BiFeO3 ultrathin film by applying external electric field. Spin-up carriers appear to the surface with positive field while spin-down ones to the negative field surface, arising from the redistribution of Fe-t2g orbital. The half-metallic behavior of Fe-3 d states in the surface of rhombohedral phase film makes it a promising candidate for antiferromagnetic/ferromagnetic bilayer heterostructure possessing electric field tunable ferromagnetic magnetization reversal and opens a new way towards designing spintronic multiferroics. The interface exchange-bias effect in this BiFeO3/ferromagnetic bilayer is mainly driven by the Fe-t2g orbital reconstruction, as well as spin transferring and rearrangement.

Spin-polarized carrier populations in diluted magnetic semiconductor quantum well structures (abstract)

Diluted magnetic semiconductors (DMS) offer the opportunity to significantly alter heterojunction band offsets via an applied magnetic field due to the large Zeeman splittings (enhanced g-factors) they exhibit. We have previously reported field-dependent spatial spin segregation of holes in DMS quantum well structures1,2 which resulted from the small band offset and large spin splitting exhibited by the valence band. We report here the growth of tailored Zn1−xFexSe/ZnSe quantum well structures in which both electrons and holes are spatially segregated according to their spin, resulting in spin-polarized carrier populations in the barriers and wells: the spin-down carriers are localized in the Zn1−xFexSe barriers, while the spin-up carriers are localized in the wells. Both single and multiple quantum well samples were grown by molecular-beam epitaxy on GaAs(001) substrates with 100 Å barriers and wells. The heavy-hole excitonic transitions were studied with magnetoreflectivity at T=4.2 K and fields up to 8 T. The magnetoreflectivity data show that both (−3/2→−1/2) and (3/2→1/2) excitonic transitions are of equal intensity and spatially direct (type I), with the former showing the strong field dependence expected for localization in the magnetically active barriers.

The anomalous hall effect in nickel alloys: Contributions from skew scattering and side displacement in the two-current model

The anomalous Hall angle in ferromagnetic alloys contains two contributions, skew scattering and side displacement both of which depend on the source of electrical resistivity: φ an = φ sk + bϱ. Experimental data on φ an for 250 binary and ternary nickel based alloys are analysed in terms of the two-current model. For a large number of solute metals, values for φ ↑ sk and φ ↓ sk are derived. It is observed that the value of b varies systematically with the fraction of the current carri ed by spin-up carriers. The results suggest that φ ↓ sk and b ↓ sk are of the same (positive) sign, while for the opposite spin direct ion they are both negative.