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Memory-functionality superconductor/ferromagnet/superconductor junctions based on the high-Tc cuprate superconductors YBa2Cu3O7-x and the colossal magnetoresistive manganite ferromagnets La2/3X1/3MnO3+δ (X = Ca, Sr)
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. University of Fribourg, Switzerland.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
Vise andre og tillknytning
Rekke forfattare: 62019 (engelsk)Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 21, artikkel-id 214510Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Complex oxides exhibit a variety of unusual physical properties, which can be used for designing novel electronic devices. Here we fabricate and study experimentally nanoscale superconductor/ferromagnet/superconductor junctions with the high-T-c cuprate superconductors YBa2Cu3O7-x and the colossal magnetoresistive (CMR) manganite ferromagnets La2/3X1/3MnO3+delta (X=Ca or Sr). We demonstrate that in a broad temperature range the magnetization of a manganite nanoparticle, forming the junction interface, switches abruptly in a monodomain manner. The CMR phenomenon translates the magnetization loop into a hysteretic magnetoresistance loop. The latter facilitates a memory functionality of such a junction with just a single CMR ferromagnetic layer. The orientation of the magnetization (stored information) can be read out by simply measuring the junction resistance in a finite magnetic field. The CMR facilitates a large readout signal in a small applied field. We argue that such a simple single-layer CMR junction can operate as a memory cell both in the superconducting state at cryogenic temperatures and in the normal state up to room temperature.

sted, utgiver, år, opplag, sider
2019. Vol. 99, nr 21, artikkel-id 214510
HSV kategori
Forskningsprogram
fysik
Identifikatorer
URN: urn:nbn:se:su:diva-171104DOI: 10.1103/PhysRevB.99.214510ISI: 000473009200002OAI: oai:DiVA.org:su-171104DiVA, id: diva2:1343571
Tilgjengelig fra: 2019-08-17 Laget: 2019-08-17 Sist oppdatert: 2019-09-11bibliografisk kontrollert
Inngår i avhandling
1. Pulsed laser deposition and nanofabrication of mesoscopic devices based on cuprates and manganites
Åpne denne publikasjonen i ny fane eller vindu >>Pulsed laser deposition and nanofabrication of mesoscopic devices based on cuprates and manganites
2019 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

This thesis explores the growth, the nano-fabrication and the study of the magneto-transport properties of Superconductor/Ferromagnet/Superconductor (SFS) structures from complex oxides such as the high Tc superconducting cuprate YBa2Cu3O7 (YBCO) and the ferromagnetic manganites La2/3Ca1/3MnO3 and La2/3Sr1/3MnO3 (LCMO and LSMO), deposited with the pulsed laser deposition (PLD) technique.The present work has been possible thanks to the collaboration between the “Magnetism and Superconductivity” Group at the University of Fribourg, in Switzerland, and the “Experimentell Kondenserade Materiens Fysik” Group at Stockholm University, in Sweden.

Earlier, the two research groups in Fribourg and Stockholm had studied SFS structures from YBCO/LaMnO3/YBCO multilayers with 20 nm thick ferromagnetic and insulating LaMnO3 barriers, and obtained signs of an unconventional spin-triplet current across these structures. This finding motivated the present thesis work with a focus on two main aspects.

Firstly, to explore other candidate materials suitable as barriers and optimise their growth conditions as to maintain a large ferromagnetic moment and thus a high spin polarisation of the charge carriers. Secondly, to study what happens when the thickness of the ferromagnetic and insulating LaMnO3 barrier is reduced well below 20 nm to enable larger supercurrents.

It has been shown for a series of YBCO/LCMO multilayers that the ferromagnetic moment of LCMO depends critically on the PLD growth conditions as well as on the thickness and even structural details of the YBCO layer on which they are grown. Furthermore, a protocol has been established to grow heterostructures with strongly ferromagnetic manganite layers embedded in thick YBCO layers by optimising the PLD growth conditions and by substituting the bottom YBCO layer with a Co and Ca substituted version of YBCO that has a tetragonal structure (tYBCO) instead of the orthorhombic one of plain YBCO.

Devices suitable for perpendicular magneto-transport measurements have been nano-fabricated from YBCO/manganite/YBCO multilayers with ~10 nm thick LCMO and LSMO layers as the F barriers. While no clear indications of a spin-triplet component of the superconducting order parameter have been obtained yet, a negative and hysteretic magneto-resistance has been observed that is indicative of a strong ferromagnetic order in the thin manganite barrier. The latter suggests a potential memory functionality of such structures that could be exploited in future spintronic memory devices.

Moreover, devices have been fabricated on SFS structures with a reduced thickness of the LaMnO3 barrier of 10 nm and 5 nm. These samples were grown prior to the beginning of this PhD work using non optimised growth conditions, and it was found that the ferromagnetic properties of these LaMnO3 barriers are strongly deteriorated. It remains to be seen whether the ferromagnetic order of such thin LaMnO3 layers can be also recovered by using the optimised growth conditions as for LSMO and LCMO.

sted, utgiver, år, opplag, sider
Stockholm: Department of Physics, Stockholm University, 2019. s. 109
Emneord
cuprates, manganites, pulsed laser deposition, nano-fabrication, heterostructures
HSV kategori
Forskningsprogram
fysik
Identifikatorer
urn:nbn:se:su:diva-172861 (URN)978-91-7797-833-6 (ISBN)978-91-7797-834-3 (ISBN)
Disputas
2019-10-28, FP41, hus 1, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (engelsk)
Opponent
Veileder
Merknad

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.

Tilgjengelig fra: 2019-10-03 Laget: 2019-09-11 Sist oppdatert: 2019-09-24bibliografisk kontrollert

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