6 Search Results

The Co-rich end of the Co–Tb binary phase diagram (CoxTb1−x, x = 0.66–0.82) has been investigated to understand the phases which form in the bulk and how they interact to yield magnetic behavior which has been reported to be ideal for use in spintronic devices. This work shows that the phases and phase fractions present across this composition range follow those predicted by the binary phase diagram, and all compounds in this composition range are multiphase. Magnetic measurements show similar behavior in this composition range to related thin film work, and we attribute the observed behavior to the respective binary phases presentmore » in each compound. Ideal magnetic behavior of minimized magnetic saturation and maximized coercivity is observed in the range of x=0.78−0.80 related to the majority phase Co7Tb2 in these two compounds. High pressure magnetic measurements show magnetic saturation and coercivity at 300 K change little with respect to external pressure. The extension of the synthesis of these binaries into the bulk allows for specific binary phases to be targeted and analyzed for consideration in future devices.« less

The binary compound V₃Ga can exhibit two near-equilibrium phases, the A15 structure that is superconducting and the Heusler D0₃ structure that is semiconducting and antiferromagnetic. Density functional theory calculations show that these two phases are nearly degenerate, being separated in energy by only ±10 meV/atom. Our magnetization measurements on bulk-grown samples show antiferromagnetism and superconducting behavior below 14 K. Overall, these results indicate the possibility of using V₃Ga for quantum technology devices exploiting the co-existence of superconductivity and antiferromagnetism in a dual-phase material.

The effects of chemical disorder on the electronic 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 L2₁ or Y phase. High temperature resistivity measurements confirm the existence of a bandgap. 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 aremore » preserved in the presence of L2₁ disorder (Cr and V mixing). 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.« less

We find that annealing a previously chemically etched interferometer at 800 °C dramatically increased the interference fringe visibility from 23% to 90%. The Bragg plane misalignments were also measured before and after annealing using neutron rocking curves, showing that Bragg plane alignment was improved across the interferometer after annealing. Furthermore, this suggests that current interferometers with low fringe visibility may be salvageable and that annealing may become an important step in the fabrication process of future neutron interferometers, leading to less need for chemical etching and larger more exotic neutron interferometers.

Recently, theorists have predicted many materials with a low magnetic moment and large spin-polarization for spintronic applications. These compounds are predicted to form in the inverse Heusler structure; however, many of these compounds have been found to phase segregate. In this study, ordered Cr₂CoGa thin films were synthesized without phase segregation using molecular beam epitaxy. The present as-grown films exhibit a low magnetic moment from antiferromagnetically coupled Cr and Co atoms as measured with superconducting quantum interface device magnetometry and soft X-ray magnetic circular dichroism. Electrical measurements demonstrated a thermally-activated semiconductor-like resistivity component with an activation energy of 87 meV.more » Finally, these results confirm spin gapless semiconducting behavior, which makes these thin films well positioned for future devices.« less