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Lenk D, Zdravkov VI, Kehrle JM, Obermeier G, Ullrich A, Morari R, Krug von Nidda HA, Müller C, Kupriyanov MY, Sidorenko AS, Horn S, Deminov RG, Tagirov LR, Tidecks R. Thickness dependence of the triplet spin-valve effect in superconductor-ferromagnet-ferromagnet heterostructures. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2016; 7:957-969. [PMID: 27547613 PMCID: PMC4979884 DOI: 10.3762/bjnano.7.88] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Accepted: 06/13/2016] [Indexed: 06/06/2023]
Abstract
BACKGROUND In nanoscale layered S/F1/N/F2/AF heterostructures, the generation of a long-range, odd-in-frequency spin-projection one triplet component of superconductivity, arising at non-collinear alignment of the magnetizations of F1 and F2, exhausts the singlet state. This yields the possibility of a global minimum of the superconducting transition temperature T c, i.e., a superconducting triplet spin-valve effect, around mutually perpendicular alignment. RESULTS The superconducting triplet spin valve is realized with S = Nb a singlet superconductor, F1 = Cu41Ni59 and F2 = Co ferromagnetic metals, AF = CoO x an antiferromagnetic oxide, and N = nc-Nb a normal conducting (nc) non-magnetic metal, which serves to decouple F1 and F2. The non-collinear alignment of the magnetizations is obtained by applying an external magnetic field parallel to the layers of the heterostructure and exploiting the intrinsic perpendicular easy-axis of the magnetization of the Cu41Ni59 thin film in conjunction with the exchange bias between CoO x and Co. The magnetic configurations are confirmed by superconducting quantum interference device (SQUID) magnetic moment measurements. The triplet spin-valve effect has been investigated for different layer thicknesses, d F1, of F1 and was found to decay with increasing d F1. The data is described by an empirical model and, moreover, by calculations using the microscopic theory. CONCLUSION The long-range triplet component of superconducting pairing is generated from the singlet component mainly at the N/F2 interface, where the amplitude of the singlet component is suppressed exponentially with increasing distance d F1. The decay length of the empirical model is found to be comparable to twice the electron mean free path of F1 and, thus, to the decay length of the singlet component in F1. Moreover, the obtained data is in qualitative agreement with the microscopic theory, which, however, predicts a (not investigated) breakdown of the triplet spin-valve effect for d F1 smaller than 0.3 to 0.4 times the magnetic coherence length, ξF1.
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Affiliation(s)
- Daniel Lenk
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
| | - Vladimir I Zdravkov
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
- D. Ghitsu Institute of Electronic Engineering and Nanotechnologies ASM, Academiei Str. 3/3, MD2028 Kishinev, Moldova
| | - Jan-Michael Kehrle
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
| | - Günter Obermeier
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
| | - Aladin Ullrich
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
| | - Roman Morari
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
- D. Ghitsu Institute of Electronic Engineering and Nanotechnologies ASM, Academiei Str. 3/3, MD2028 Kishinev, Moldova
- Solid State Physics Department, Kazan Federal University, Kremlevskaya Str. 18, 420008 Kazan, Russian Federation
| | | | - Claus Müller
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
| | - Mikhail Yu Kupriyanov
- Solid State Physics Department, Kazan Federal University, Kremlevskaya Str. 18, 420008 Kazan, Russian Federation
- Skobeltsyn Institute of Nuclear Physics, Moscow State University, Leninskie gory, GSP-1, Moscow 119992, Russia
| | - Anatolie S Sidorenko
- D. Ghitsu Institute of Electronic Engineering and Nanotechnologies ASM, Academiei Str. 3/3, MD2028 Kishinev, Moldova
| | - Siegfried Horn
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
| | - Rafael G Deminov
- Solid State Physics Department, Kazan Federal University, Kremlevskaya Str. 18, 420008 Kazan, Russian Federation
| | - Lenar R Tagirov
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
- Solid State Physics Department, Kazan Federal University, Kremlevskaya Str. 18, 420008 Kazan, Russian Federation
| | - Reinhard Tidecks
- Institut für Physik, Universität Augsburg, Universitätsstraße 1, D-86159 Augsburg, Germany
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Laver M, Forgan EM, Brown SP, Charalambous D, Fort D, Bowell C, Ramos S, Lycett RJ, Christen DK, Kohlbrecher J, Dewhurst CD, Cubitt R. Spontaneous symmetry-breaking vortex lattice transitions in pure niobium. PHYSICAL REVIEW LETTERS 2006; 96:167002. [PMID: 16712261 DOI: 10.1103/physrevlett.96.167002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2005] [Indexed: 05/09/2023]
Abstract
We report an extensive investigation of magnetic vortex lattice (VL) structures in single crystals of pure niobium with the magnetic field applied parallel to a fourfold symmetry axis, so as to induce frustration between the cubic crystal symmetry and hexagonal VL coordination expected in an isotropic situation. We observe new VL structures and phase transitions; all the VL phases observed (including those with an exactly square unit cell) spontaneously break some crystal symmetry. One phase even has the lowest possible symmetry of a two-dimensional Bravais lattice. This is quite unlike the situation in high-Tc or borocarbide superconductors, where VL structures orient along particular directions of high crystal symmetry. The causes of this behavior are discussed.
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Affiliation(s)
- M Laver
- Institut Laue-Langevin, BP 156, F-38042 Grenoble, France
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Stan G, Field SB, Martinis JM. Critical field for complete vortex expulsion from narrow superconducting strips. PHYSICAL REVIEW LETTERS 2004; 92:097003. [PMID: 15089502 DOI: 10.1103/physrevlett.92.097003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2002] [Indexed: 05/24/2023]
Abstract
We have measured the maximum field for which vortices are completely expelled from a thin-film superconducting strip. Niobium strips of width W were field cooled and imaged with a scanning Hall-probe microscope. Below a critical field B(m) approximately Phi(0)/W(2) all flux was expelled; above this field vortices were observed with a density increasing approximately linearly with field. The small value of the critical field, which is orders of magnitude less than in the bulk, implies that superconducting devices should be designed with narrow wires to eliminate the generation of noise from vortex motion.
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Affiliation(s)
- Gheorghe Stan
- Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA
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Guichard W, Aprili M, Bourgeois O, Kontos T, Lesueur J, Gandit P. Phase sensitive experiments in ferromagnetic-based Josephson junctions. PHYSICAL REVIEW LETTERS 2003; 90:167001. [PMID: 12731993 DOI: 10.1103/physrevlett.90.167001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2002] [Indexed: 05/24/2023]
Abstract
We have measured the ground state of ferromagnetic Josephson junctions using a single dc SQUID (superconducting quantum interference device).We show that the Josephson coupling is either positive (0 coupling) or negative (pi coupling) depending on the ferromagnetic layer thickness. As expected, the sign change of the Josephson coupling is observed as a shift of half a quantum flux in the SQUID diffraction pattern when operating in the linear limit.
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Affiliation(s)
- W Guichard
- CRTBT-CNRS, 25 Avenue des Martyrs, 38042 Grenoble, France
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