Upper critical fields of ferromagnet/superconductor layered structures

Krunavakarn, B.; Yoksan, S.

doi:10.1016/j.physc.2006.03.036

Cited by 23 publications

(19 citation statements)

References 49 publications

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“…For a uniform magnetic field we choose the gauge A = (0, Hx, 0) and employ the following Ansatz for the anomalous Green function and the order parameter [30],…”

Section: Parallel Upper Critical Fieldmentioning

confidence: 99%

“…An approximate single-mode analysis for the critical field [28] was further developed in Ref. [30], where rigorous solution of the quasiclassical Usadel equations [31] was worked out both for SF-bilayers and for SF-multilayers. These theoretical studies of the critical fields are important not only because of possible influence of the pivoting field on the onset of superconductivity in the system, but in view of justifying the consistency of the FFLO [32,33] physics, implemented into the Usadel formalism, with the actual experiments.…”

Section: Introductionmentioning

confidence: 99%

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Experimental and theoretical analysis of the upper critical field in ferromagnet–superconductor–ferromagnet trilayers

Antropov¹,

Kalenkov²,

Kehrle³

et al. 2013

Supercond. Sci. Technol.

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Abstract. The upper critical magnetic field H c2 in thin-film FSF trilayer spinvalve cores is studied experimentally and theoretically in geometries perpendicular and parallel to the heterostructure surface. The series of samples with variable thicknesses d F1 of the bottom and d F2 of the top Cu 41 Ni 59 F-layers are prepared in a single run, utilizing a wedge deposition technique. The critical field H c2 is measured in the temperature range 0.4 − 8 K and for magnetic fields up to 9 Tesla. A transition from oscillatory to reentrant behavior of the superconducting transition temperature versus F-layers thickness, induced by an external magnetic field, has been observed for the first time. In order to properly interpret the experimental data, we develop a quasiclassical theory, enabling one to evaluate the temperature dependence of the critical field and the superconducting transition temperature for an arbitrary set of the system parameters. A fairly good agreement between our experimental data and theoretical predictions is demonstrated for all samples, using a single set of fit parameters. This confirms adequacy of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) physics in determining the unusual superconducting properties of the studied Cu 41 Ni 59 /Nb/Cu 41 Ni 59 spin-valve core trilayers.Experimental and theoretical analysis of the upper critical field in FSF trilayers 2

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“…For a uniform magnetic field we choose the gauge A = (0, Hx, 0) and employ the following Ansatz for the anomalous Green function and the order parameter [30],…”

Section: Parallel Upper Critical Fieldmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental and theoretical analysis of the upper critical field in ferromagnet–superconductor–ferromagnet trilayers

Antropov¹,

Kalenkov²,

Kehrle³

et al. 2013

Supercond. Sci. Technol.

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“…Finally, not only T c but also upper critical magnetic fields in S/F heterostructures have been theoretically predicted to oscillate as a function of d F due to the presence of the -phase difference between two S layers 15,16 but no experimental evidence of these predictions have been reported so far. Most of the papers devoted to upper critical magnetic fields measurements in S/F hybrids reported, in fact, on the study of coupling phenomena between the superconducting layers and on the analysis of the dimensional crossover in the temperature dependence of the parallel critical field.…”

mentioning

confidence: 99%

“…16,32 The authors calculate the reduced perpendicular and parallel critical fields at zero temperature as a function of the reduced thickness taking also into account the effect of the interface transparency T. If the data reported in reflecting interface ͑T =0͒ and it is equal to 0 for a perfect transparent interface ͑T = ϱ͒. It is interesting to note that in both cases the curves are nonmonotonic showing a maximum which goes to higher d F / F ‫ء‬ values for higher values of the interface transparency.…”

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confidence: 99%

Nonmonotonic behavior of the anisotropy coefficient in superconductor-ferromagnet-superconductor trilayers

et al. 2009

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We have measured critical temperatures and upper critical magnetic fields as a function of the ferromagnetic layer thickness, d F , in two different superconductor͑S͒/ferromagnet͑F͒/superconductor͑S͒ triple layers: Nb/ Cu 0.41 Ni 0.59 / Nb and Nb/ Pd 0.81 Ni 0.19 / Nb. We vary d F from the 0-phase coupling to the -phase coupling regime and find strong nonmonotonic behavior of the anisotropy coefficient ␥ GL = H c2ʈ ͑0͒ / H c2Ќ ͑0͒ characterized by an initial increase, a peak, and a subsequent decrease. The peak is a manifestation of the small coupling which exists around the 0-transition and it is qualitatively in agreement with recent theoretical predictions ͓B. Krunavakarn and S. Yoksan, Physica C 440, 25 ͑2006͔͒ which includes the effect of the different interface transparencies of the two systems. The experimental results demonstrate that the occurrence of the phase strongly influences the transport properties of S/F/S systems in external fields. The proximity effect in superconductor ͑S͒/ferromagnet ͑F͒ hybrids has recently attracted a lot of interest due to the inhomogeneous nature of the superconducting order parameter in these structures.1-3 One of the most relevant consequences of the peculiar character of the order parameter is the nonmonotonic behavior of the superconducting critical temperature T c as a function of the thickness d F of the F layer which has been observed in many S/F heterostructures.4-6 Also, in the so-called S/F/S Josephson junctions negative critical currents have been measured. [7][8][9] What essentially happens is that the interaction of the Cooper pairs with the exchange field E ex causes the order parameter to oscillate on the F side of the interface over a distance F , the coherence length in the ferromagnet. On the other hand, on the S side, the order parameter is strongly suppressed over a distance of the order of the superconducting coherence length S , which, in conventional superconductors such as Nb, is usually of a few nanometers. In weak ferromagnetic alloys such as PdNi and CuNi, due to the smaller value of E ex , F is of the order of some nanometers. In the dirty limitwhere D F is the diffusion coefficient of the F metal. Another characteristic length introduced when studying S/F hybrids is F ‫ء‬ = ͱ បD F / 2k B T c which is a measure of the diffusive motion of the Cooper pairs in the ferromagnet and which will be needed in order to compare our data with theoretical calculations. However, the strength of the proximity effect between the S and F layers depends also on the quality of the interfaces. An important parameter in the theoretical description therefore is the interface transparency, T.10,11 Its influence on the behavior of the T c both as a function of the thickness d S of the S layer and of d F has been studied both in Nb/CuNi and Nb/PdNi bilayers 12,13 and also, more recently, the behavior of the parallel upper critical field in these systems has been considered.14 All these studies revealed a somehow higher value of the interface transparency in the Nb/PdN...

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“…In the presence of the external magnetic field H = rotA and triplet correlations, the pair amplitudeF satisfies the Usadel-like equations [21,[26][27][28] …”

Section: Main Equationsmentioning

confidence: 99%

A Peculiar Solitary Re-entrant Superconductivity Induced by an External Magnetic Field in Ferromagnet-Superconductor Heterostructures

Proshin

Avdeev

2014

J Low Temp Phys

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We solve the boundary value problem for the Usadel-like equations in the dirty limit case for thin-film three-layered ferromagnet (F) -superconductor (S) structures. Our theoretical approach taking into account of the asymmetry and triplet superconducting correlations is valid in the external magnetic field presence as in the real experimental setup for the FS spin valve explorations. Based on the recent experimental data obtained for the symmetrical (FSF) trilayer in an external magnetic field, we expand the theoretical description to the asymmetrical FSF and FFS trilayers. We also consider the peculiar re-entrant superconductivity and solitary superconductivity induced by the external magnetic field for the FFS trilayer.

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Upper critical fields of ferromagnet/superconductor layered structures

Cited by 23 publications

References 49 publications

Experimental and theoretical analysis of the upper critical field in ferromagnet–superconductor–ferromagnet trilayers

Experimental and theoretical analysis of the upper critical field in ferromagnet–superconductor–ferromagnet trilayers

Nonmonotonic behavior of the anisotropy coefficient in superconductor-ferromagnet-superconductor trilayers

A Peculiar Solitary Re-entrant Superconductivity Induced by an External Magnetic Field in Ferromagnet-Superconductor Heterostructures

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