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Half-metallic single-crystal CrO2 films with nearly 100% spin polarization
Y. Ji, G. J. Strijkers, F. Y. Yang, C. L. Chien, J. M. Byers, A. Anguelouch, G. Xiao and A. Gupta
Electrons have both charge and spin. However, traditional electronic devices have utilized only the transport and storage of electronic charge. Recent advances have led to the development of next generation devices, the spintronic or magneto-electronic devices, that manipulate both the charge and the spin of the electrons.
Crucial to all spintronic devices are materials with a high spin polarization. Ordinary metals, such as copper, have zero spin polarization, whereas ferromagnetic metals, such as iron, have spin polarization of about 40% or less. The ultimate spin-polarized materials attainable are the so-called half-metallic ferromagnets (HMF) which are 100% spin polarized.
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We have used the technique of point-contact Andreev reflection with proper analyses to determine the spin polarization of single-crystal CrO2 via the density of states of a superconductor. We have observed spin polarization of at least 96%, the highest reported to date in any material, in single-crystal CrO2 thin films made by MRSEC researchers at Brown University and IBM using chemical vapor deposition.
When HMFs, such as CrO2, are made into magnetic tunnel junctions, they have the potential to yield the ultimate in a new class of circuit elements and non-volatile memory chips.
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(a)-(d)Measured conductance G(Vb)/Gn vs. bias voltage Vb
of Pb/CrO2 point contacts at 1.85 K. (e) spin polarization as a
function of Z, which is a measure of surface scattering.
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