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Accueil > Evénements > Séminaires > Archives 2015 > Scanning SQUID-on-tip
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Séminaire général de l’INSP

Scanning SQUID-on-tip microscopy, magnetic imaging at the nanoscale - Yonathan Anahory - Jeudi 26 mars 2015 à 16 h 30

INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-23 - 3e étage, salle 317

Yonathan Anahory - Department of Condensed Matter Physics, Weizmann Institute of Science (Israel)

Abstract

NanoSQUIDs residing on the apex of a quartz tip (SOT), suitable for scanning probe microscopy with record size, spin sensitivity, and operating magnetic fields, are presented[1]. We have developed SOT made of Pb with an effective diameter of 46 nm and flux noise of Φn = 50 nΦ0/Hz1/2 at 4.2 K that is operational up to unprecedented high fields of 1 T[2]. The corresponding spin sensitivity of the device is Sn = 0.38 μB/Hz1/2, which is about two orders of magnitude more sensitive than any other SQUID to date. This new device paves the way to magnetic imaging of numerous nanoscaled systems exhibiting exciting physics. One of the systems we studied is vortex matter in superconductors. At low vortex density and low currents, we measure the fundamental dependence of the elementary pinning force of multiple defects on the vortex displacement. The outstanding magnetic sensitivity of the SOT allows probing vortex displacements as small as 10 pm[3]. This study reveals rich internal structure of the pinning potential and unexpected phenomena such as softening of the restoring force and abrupt depinning. The results shed new light on the importance of multi-scale random disorder on vortex dynamics and thermal relaxation. At high vortex density and high currents, we image the flow patterns of moving lattice revealing dynamic instabilities, plastic flow, and ordering. Another system we studied is an atomically sharp layer of LaMnO3 on a SrTiO3 substrate. Using the high spatial resolution of the scanning SOT microscope, we able to resolved magnetic structures smaller than 100 nm. We observe a clear enhancement of the ferromagnetic signal when the LaMnO3 layer is larger than 5 unit cell. The magnetization field dependence suggests that a ferromagnetic and anti-ferromagnetic phase coexists. The ferromagnetic phase forms nanometer size droplets that are embedded in an anti-ferromagnetic matrix. The results will be interpreted in terms of a first principle model.

[1] A. Finkler, Y. Segev, Y. Myasoedov, M. L. Rappaport, L. Neeman, D. Vasyukov, E. Zeldov, M. E. Huber, J. Martin and A. Yacoby, Nano Lett. 10, 1046 (2010)
[2] D. Vasyukov, Y. Anahory, L. Embon, D. Halbertal, J. Cuppens, L. Neeman, A. Finkler, Y. Segev, Y. Myasoedov, M. L. Rappaport, M. E. Huber, and E. Zeldov, Nature Nanotech. 8, 639 (2013). [3] L. Embon, Y.Anahory, A. Suhov, D. Halbertal, J. Cuppens, A. Yakovenko, A. Uri, Y. Myasoedov, M.L. Rapparport, M.E. Huber, A. Gurevich and E. Zeldov, Scientific Reports 5 (2015) 7598