Synergy of exchange bias with superconductivity in ferromagnetic–superconducting layered hybrids: the influence of in-plane and out-of-plane magnetic order on superconductivity

Abstract

It is generally believed that superconductivity and magnetism are two antagonistic long-range phenomena. However, as it was preliminarily highlighted in D. Stamopoulos et al. [Phys. Rev. B 75, 014501 (2007)] and extensively studied in this work under specific circumstances these phenomena instead of being detrimental to each other may even become cooperative so that their synergy may promote the superconducting properties of a hybrid structure.Here, we have studied systematically the magnetic and transport behavior of such exchange biased hybrids that are comprised of ferromagnetic (FM) Ni80Fe20 and low-Tc superconducting (SC) Nb for the case where the magnetic field is applied parallel to the specimens. Two structures have been studied: FM-SC-FM trilayers (TLs) and FM-SC bilayers (BLs). Detailed magnetization data on the longitudinal and transverse magnetic components are presented for both the normal and superconducting states. These data are compared to systematic transport measurements including I-V characteristics. The comparison of the exchange biased BLs and TLs that are studied here with the plain ones studied in D. Stamopoulos et al. [Phys. Rev. B 75, 184504 (2007)] enable us to reveal an underlying parameter that may falsify the interpretation of the transport properties of relevant FM-SC-FM TLs and FM-SC BLs investigated in the recent literature: the underlying mechanism motivating the extreme magnetoresistance peaks in the TLs relates to the suppression of superconductivity mainly due to the magnetic coupling of the two FM layers as the out-of-plane rotation of their magnetizations takes place across the coercive field where stray fields emerge in their whole surface owing to the multidomain magnetic state that they acquire. The relative inplane magnetization configuration of the outer FM layers exerts a secondary contribution on the SC interlayer. Since the exchange bias directly controls the in-plane magnetic order it also controls the out-of-plane rotation of the FMs' magnetizations so that the magnetoresistance peaks may be tuned at will.All the contradictory experimental data reported in the recent literature are fairly discussed under the light of our results; based on a specific prerequisite we propose a phenomenological strayfields mechanism that explains efficiently the evolution of magnetoresistance effect in TLs. Our experiments not only point out the need for a new theoretical treatment of FM-SC hybrids but also direct us toward the design of efficient supercurrent-switch elemental devices.

Modulation of the properties of thin ferromagnetic films with an externally applied electric field in ferromagnetic/piezoelectric/ferromagnetic hybrids

“…From the study of relevant artificial structures of heterogeneous constituents, [1][2][3][4][5][6][7][8][9][10][11][12] it is well known that any effect occurring by the interface of layered hybrids has only limited range, thus penetrating at a length scale ranging between a few nanometers to a few tens of nanometers at the interior of each constituent layer. Following this guideline, for the FM/PE/FM hybrids studied here, the FM outer layers should have the lowest possible thickness since this will ensure that the part of the Co layers affected from the strain provided by the PE crystal will be the maximum.…”

“…For instance, the modulation of the properties of a superconductor (SC) by the exchange field (superconducting spin valve effect) and/or stray fields (superconducting magnetoresistance effect) provided by an adjacent ferromagnet (FM) has been studied in great detail both experimentally [1][2][3][4][5] and theoretically 6,7 in various versions of SC/FM hybrids. Another example comes from the field of exchange bias where the exchange coupling between a FM and an adjacent antiferromagnet is effective only in the limit of thin films since the cornerstone macroscopic parameter involved in this effect, the so-called exchange bias field, is inversely proportional to the thickness of the FM layer due to the limited penetration of the coupling field inside its interior.…”

Exchange-bias-modulated inverse superconducting spin switch inCoO/Co/YBa2Cu3O7−δNemes1, Visani2, Sefrioui3 et al. 2010Phys. Rev. B5000View full textAdd to dashboardCite

“…Then we show the magnetoresistance of various bilayers, as they can be considered the constituent parts of a trilayer, although with the caveat that in a trilayer, the two F electrodes might be coupled magnetostatically. 16 Finally, we return to the trilayer and present its magnetoresistance and magnetization both immediately after deposition and after 2 weeks of aging.…”

“…9,37 The smaller MR values at the plateau ͑30%-100%͒ in LCMO/YBCO/Co as compared to the large values found in symmetric LCMO/YBCO/LCMO trilayers in excess of 300% at similar R min / R n may be related to the smaller degree of spin polarization of the conduction band of the Co ͑34%͒ contrary to the high spin polarization of LCMO. 38,39 The effect of stray fields on the superconducting state has been extensively discussed by Steiner and Ziemann and by Stamopoulos et al 12,16 Steiner and Ziemann studied F / S bilayers ͑Nb/Fe͒, F/ S / F trilayers ͑Co/Nb/Fe͒, and EB-F/ S / F exchange biased trilayers ͑CoO/Co/Nb/Fe͒. They found positive MR peaks ͑or equivalently depressions of T c ͒ at the coercive field͑s͒ of the ferromagnet͑s͒ in bilayers and trilayers and proposed that they originate in the micromagnetic stray fields of the ferromagnetic layers.…”

“…In structures combining transition-metal ferromagnets and low-T c superconductors, this has been accomplished by means of pinning the magnetization of one of the layers via exchange bias in exchange spring structures. 12,16 In these cases, the antiferromagnet ͑AF͒ of the AF/F exchange bias structures was produced by in situ oxidation of one of the F layers. In this way, Steiner and Ziemann 12 and also Stamopoulos et al 13 showed MR peaks at the coercive fields due to the action of stray fields.…”