Thermodynamics and phase diagrams of layered superconductor/ferromagnet nanostructures

Barsic, Paul H.; Valls, Oriol T.; Halterman, Klaus

doi:10.1103/physrevb.75.104502

Cited by 32 publications

(57 citation statements)

References 47 publications

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“…In particular, the theoretical method we used to find T c can be found in Refs. [32,33]. We modeled the Nb/Co/Cu/Co heterostructures as S/F f /N/F p layered systems, where S represents the superconducting layer, F f and F p are the inner (free) and outer (pinned) magnets, and N denotes the normal metallic intermediate layer.…”

Section: Theoretical Methodsmentioning

confidence: 99%

Angular dependence of superconductivity in superconductor/spin-valve heterostructures

et al. 2014

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We report measurements of the superconducting transition temperature, T c , in CoO/Co/Cu/Co/Nb multilayers as a function of the angle α between the magnetic moments of the Co layers. Our measurements reveal that T c (α) is a nonmonotonic function, with a minimum near α = π/2. Numerical self-consistent solutions of the Bogoliubov-de Gennes equations quantitatively and accurately describe the behavior of T c as a function of α and layer thicknesses in these superconductor / spin-valve heterostructures. We show that experimental data and theoretical evidence agree in relating T c (α) to enhanced penetration of the triplet component of the condensate into the Co/Cu/Co spin valve in the maximally noncollinear magnetic configuration.

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Section: Theoretical Methodsmentioning

confidence: 99%

Angular dependence of superconductivity in superconductor/spin-valve heterostructures

et al. 2014

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“…In principle, one should take into account the Fermi-surface mismatch at each interface, as well as the different densities of states, mean free paths, and diffusion constants for the majority and minority spin bands. Microscopic calculations based on the Bogoliubov-deGennes equations and taking into account the finite interface transparency, have been performed for ballistic systems 47,48 , and could, in principle, be extended to systems with disorder. But there have been no theoretical calculations of the supercurrent that take into account the complex band structure of transitionmetal ferromagnetic materials such as those discussed in this paper.…”

Section: Measurement and Analysismentioning

confidence: 99%

Critical current oscillations of elliptical Josephson junctions with single-domain ferromagnetic layers

Glick

Khasawneh

Niedzielski

et al. 2017

Journal of Applied Physics

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Josephson junctions containing ferromagnetic layers are of considerable interest for the development of practical cryogenic memory and superconducting qubits. Such junctions exhibit a ground-state phase shift of π for certain ranges of ferromagnetic layer thickness. We present studies of Nb based micron-scale ellipticallyshaped Josephson junctions containing ferromagnetic barriers of Ni 81 Fe 19 or Ni 65 Fe 15 Co 20 . By applying an external magnetic field, the critical current of the junctions are found to follow characteristic Fraunhofer patterns, and display sharp switching behavior suggestive of single-domain magnets. The high quality of the Fraunhofer patterns enables us to extract the maximum value of the critical current even when the peak is shifted significantly outside the range of the data due to the magnetic moment of the ferromagnetic layer. The maximum value of the critical current oscillates as a function of the ferromagnetic barrier thickness, indicating transitions in the phase difference across the junction between values of zero and π. We compare the data to previous work and to models of the 0-π transitions based on existing theories.

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“…7 In fact at the crossover from the 0 and the phase the nature of the coupling between the two Nb layers changes, the order parameter showing a node in the center of the F layer. 31 It is then reasonable to suppose that the coupling will be strongly reduced in this regime. For this reason around the smallest coupling the anisotropy coefficient will present a peak, which will be superimposed on the standard increase.…”

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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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Thermodynamics and phase diagrams of layered superconductor/ferromagnet nanostructures

Cited by 32 publications

References 47 publications

Angular dependence of superconductivity in superconductor/spin-valve heterostructures

Angular dependence of superconductivity in superconductor/spin-valve heterostructures

Critical current oscillations of elliptical Josephson junctions with single-domain ferromagnetic layers

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

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