The spin-filter material CrVTiAl is a promising candidate for producing highly spin-polarized currents at room temperature in a nonmagnetic architecture. Thin films of compensated-ferrimagnetic CrVTiAl have been grown and their electrical and magnetic properties have been studied. The resistivity shows two-channel semiconducting behavior with one disordered gapless channel and a gapped channel with activation energy ∆E= 0.1 -0.2 eV. Magnetoresistance measurements to B = 35 T provide values for the mobilities of the gapless channel, leading to an order of magnitude difference in the carrier effective masses, which are in reasonable accord with our density-functional-theory based results. The density of states and electronic band structure is computed for permutations of the four sublattices arranged differently along the (111) body diagonal, yielding metallic (Cr-V-Al-Ti), spin-gapless (Cr-V-Ti-Al) and spin-filtering (Cr-Ti-V-Al) phases. Robustness of the spin-gapless phase to substitutional disorder is also considered.FIG. 1. Schematic of a spin-filter device. The SFM is sandwiched between two nonmagnetic metallic contacts. As the barrier height for the electrons with different spin directions is different, the spin with the smaller band gap (barrier height) dominates the tunneling current.
The effects of chemical disorder on the transport properties of the spin-filter material CrVTiAl are investigated experimentally and theoretically. Synchrotron X-ray diffraction experiments on bulk CrVTiAl and the associated Rietveld analysis indicate that the crystal structure consists primarily of a mixture of a partially ordered B2 phase, a fully disordered A2 phase and a small component of an ordered L2 1 or Y phase. High temperature resistivity measurements confirm the existence of a band gap. First-principles, all-electron, self-consistent electronic structure computations show that the chemically disordered A2 and B2 phases are metallic, while the spin-filter properties of the ideal Y-type phase are preserved in the presence of L2 1 disorder. The Hall coefficient is found to decrease with increasing temperature, similar to the measured increase in the conductivity, indicating the presence of thermally activated semiconductor-like carriers.
Some cuprate superconductors exhibit high critical temperatures at atmospheric pressure. To understand the underlying processes, researchers recently carried out high-pressure nuclear magnetic resonance experiments on the cuprate YBa2Cu3O6+y to determine the charge densities at the Cu and O sites of its CuO2 plane with high precision. Their results revealed that the more generous the in-plane Cu atoms are in transferring their hole content to the O atoms, the higher the critical temperatures that can be achieved.
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