• Open Access

High-Quality CrO2 Nanowires for Dissipation-less Spintronics

Amrita Singh, Charlotte Jansen, Kaveh Lahabi, and Jan Aarts
Phys. Rev. X 6, 041012 – Published 18 October 2016
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Abstract

Superconductor-ferromagnet (S-F) hybrids based on half-metallic ferromagnets, such as CrO2, are ideal candidates for superconducting spintronic applications. This is primarily due to the fully spin-polarized nature of CrO2, which produces enhanced long-range triplet proximity effects. However, reliable production of CrO2-based Josephson junctions (JJs) has proved to be extremely challenging because of a poorly controlled interface transparency and an incomplete knowledge of the local magnetization of the CrO2 films. To address these issues, we use a bottom-up approach to grow CrO2 nanowires on prepatterned substrates via chemical-vapor deposition. A comprehensive study of the growth mechanism enables us to reliably synthesize faceted, homogeneous CrO2 wires with a well-defined magnetization state. Combining these high-quality wires with a superconductor produces JJs with a high interface transparency, leading to exceptionally large 100% spin-polarized supercurrents, with critical current densities exceeding 109Am2 over distances as long as 600 nm. These CrO2-nanowire-based JJs thus provide a realistic route to creating a scalable device platform for dissipation-less spintronics.

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  • Received 29 June 2016

DOI:https://doi.org/10.1103/PhysRevX.6.041012

Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Amrita Singh, Charlotte Jansen, Kaveh Lahabi, and Jan Aarts*

  • Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands

  • *aarts@physics.leidenuniv.nl

Popular Summary

Spin is a potential degree of freedom for storing information in next-generation spintronics devices. One way to manipulate such spins would be to use a spin-polarized current, but dissipation is then a serious problem. This limitation can potentially be remedied using spin-polarized supercurrents. Hybrid structures composed of superconductors and ferromagnets can be used for this purpose, but a lack of control over the mechanism to induce the supercurrent in a ferromagnetic wire has inhibited efforts to achieve reliable spintronics devices. Here, we demonstrate that sub-micron-sized wires of 100% spin-polarized CrO2 (a half-metallic ferromagnet), combined with superconductors, can create Josephson junctions that can carry record-high spin-polarized supercurrents over length scales of several hundred nanometers.

We start by growing faceted CrO2 nanowires using chemical vapor deposition and selective area growth to create homogeneous and highly crystalline wires. In this way, we achieve control over both the morphology and magnetization of the nanowires, and we demonstrate these results using atomic force microscopy and magnetic force microscopy. By combining such wires with a superconductor, we create supercurrents in the spin-polarized CrO2 that inhibit dissipation. We find that our setup with CrO2 is roughly 100 times more effective at inducting supercurrents than with conventional ferromagnets such as Ni, Co, or Fe.

Our findings provide the first seriously viable route toward building scalable device architectures for superconducting spintronics.

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Issue

Vol. 6, Iss. 4 — October - December 2016

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