Doppler-scanning tunneling microscopy current imaging in superconductor-ferromagnet hybrids

Moore, Steven A.; Plummer, Gabriel; Fedor, J.; Pearson, John; Novosad, V.; Karapetrov, G.; Iavarone, M.

doi:10.1063/1.4940190

Cited by 6 publications

(5 citation statements)

References 36 publications

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“…An alternative way to detect the currents associated with these spontaneous magnetic fields can be based on the use of different types of local transport probes positioned at the outer boundary of the superconductor. Scanning, e.g., the outer surface by the normal metal tip of the scanning tunneling microscope one can measure the changes in the local density of states caused by the Doppler shift of the quasiparticles energy in the presence of the superflow [22][23][24] . For the case of the superconducting probe one can also propose a simple and elegant experimental setup revealing this effect.…”

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confidence: 99%

Electromagnetic proximity effect in planar superconductor-ferromagnet structures

Миронов

Mel’nikov

Buzdin

2018

Applied Physics Letters

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The spread of the Cooper pairs into the ferromagnet in proximity coupled superconductor -ferromagnet (SF) structures is shown to cause a strong inverse electromagnetic phenomenon, namely, the long-range transfer of the magnetic field from the ferromagnet to the superconductor. Contrary to the previously investigated inverse proximity effect resulting from the spin polarization of superconducting surface layer, the characteristic length of the above inverse electrodynamic effect is of the order of the London penetration depth, which usually much larger than the superconducting coherence length. The corresponding spontaneous currents appear even in the absence of the stray field of the ferromagnet and are generated by the vector-potential of magnetization near the S/F interface and they should be taken into account at the design of the nanoscale S/F devices. Similarly to the well-known Aharonov-Bohm effect, the discussed phenomenon can be viewed as a manifestation of the role of vector potential in quantum physics.

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confidence: 99%

Electromagnetic proximity effect in planar superconductor-ferromagnet structures

Миронов

Mel’nikov

Buzdin

2018

Applied Physics Letters

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“…In films with a strong perpendicular magnetic anisotropy the formation of closure domains becomes energetically unfavorable. However, recent magnetic simulations, based on the measured magnetic hysteresis loops, show the appearance of closure domains in a twin Co/Pd multilayers as well59. In general, closure domains are difficult to observe because the majority of the conventional magnetic imaging techniques rely on the detection of the out-of-plane stray fields.…”

Section: Resultsmentioning

confidence: 99%

Observation of superconducting vortex clusters in S/F hybrids

Giorgio

Bobba

Cucolo

et al. 2016

Sci Rep

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While Abrikosov vortices repel each other and form a uniform vortex lattice in bulk type-II superconductors, strong confinement potential profoundly affects their spatial distribution eventually leading to vortex cluster formation. The confinement could be induced by the geometric boundaries in mesoscopic-size superconductors or by the spatial modulation of the magnetic field in superconductor/ferromagnet (S/F) hybrids. Here we study the vortex confinement in S/F thin film heterostructures and we observe that vortex clusters appear near magnetization inhomogeneities in the ferromagnet, called bifurcations. We use magnetic force microscopy to image magnetic bifurcations and superconducting vortices, while high resolution scanning tunneling microscopy is used to obtain detailed information of the local electronic density of states outside and inside the vortex cluster. We find an intervortex spacing at the bifurcation shorter than the one predicted for the same superconductor in a uniform magnetic field equal to the thermodynamical upper critical field Hc2. This result is due to a local enhanced stray field and a competition between vortex-vortex repulsion and Lorentz force. Our findings suggest that special magnetic topologies could result in S/F hybrids that support superconductivity even when locally the vortex density exceeds the thermodynamic critical threshold value beyond which the superconductivity is destroyed.

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“…The increased pinning is due to weakened superconductivity. This weakened superconductivity is due to superconducting currents induced by the local magnetic field gradients at the domain walls and edges of nanomagnets 26 , 27 .…”

Section: Introductionmentioning

confidence: 99%

“…This can be done with materials which exhibit perpendicular magnetic anisotropy (PMA). Domain size can be varied from a few nm to several m with a large variety of geometrical configurations (parallel stripes, labyrinths, bubbles, single domain …) depending on the interplay between material parameters (saturation magnetization M S , anisotropy K N and disorder), element geometry (thickness and lateral dimensions) and magnetic history [22][23][24][25][26][27][28][29][30]. In a film, domain configuration is governed by Q, the ratio of perpendicular magnetic anisotropy K N to magnetostatic energy Q= 2K N / 0 M S 2 and by the effect of disorder on nucleation and propagation processes of reversed domains [31].…”

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confidence: 99%

Magnetic order and disorder in nanomagnets probed by superconducting vortices

Rollano

Valle

Gómez

et al. 2018

Sci Rep

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We have studied two nanomagnet systems with strong (Co/Pd multilayers) and weak (NdCo alloy films) stray magnetic fields by probing the out-of-plane magnetic states with superconducting vortices. The hybrid samples are made of array of nanomagnets embedded in superconducting Nb thin films. The vortex motion detects relevant magnetic state features, since superconducting vortices are able to discriminate between different magnetic stray field strengths and directions. The usual matching effect between the superconducting vortex lattice and the periodic pinning array can be quenched by means of disorder magnetic potentials with strong stray fields at random. Ordered stray fields retrieve the matching effect and yield asymmetry and shift in the vortex dissipation signal. Furthermore vortices can discriminate the sizes of the nanomagnet magnetic domains, detecting magnetic domain sizes as small as 70 nm. In addition, we observe that the vortex cores play the crucial role instead of the supercurrents around the vortex.

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Doppler-scanning tunneling microscopy current imaging in superconductor-ferromagnet hybrids

Cited by 6 publications

References 36 publications

Electromagnetic proximity effect in planar superconductor-ferromagnet structures

Electromagnetic proximity effect in planar superconductor-ferromagnet structures

Observation of superconducting vortex clusters in S/F hybrids

Magnetic order and disorder in nanomagnets probed by superconducting vortices

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