Imaging the spontaneous formation of vortex-antivortex pairs in planar superconductor/ferromagnet hybrid structures

Abstract

Low-temperature magnetic force microscopy has been used to visualize spontaneous formation of vortex-antivortex pairs in hybrid ferromagnet/superconductor systems. Vortex-antivortex pairs are induced by the periodic stray field of the ferromagnet. We find general equilibrium conditions for which spontaneous vortex-antivortex pairs are formed during zero-field cooling of the hybrid ferromagnet/superconductor bilayers. Vortices can be generated by the ferromagnet domains in the absence of an external field and they are thermodynamically stable for values of the stray field and the period of the stripe magnetic domains that exceed a certain threshold

Irreversible magnetization switching at the onset of superconductivity in a superconductor ferromagnet hybrid

“…5 (a), are forced to quantize into superconducting vortices, (b). Here we observe the coexistence of vortices and antivortices, highlighted by black and white dots respectively, which has already been predicted, 16 and observed, 17 in SF bi-layers. In marked contrast to the behavior at T=10K, the magnetic structure remains qualitatively unchanged as the field is stepped up to 30 Oe, 5 Oe in excess of the known switching field.…”

Visualization of the magnetic flux structure in phosphorus-doped EuFe2As2 single crystals

“…Previously, the magnetic flux structure was visualized with the MFM on artificial thin-film superconductor/ferromagnet (Nb/FeNi) hybrid structures, 15 where the domain structure and Abrikosov vortices frozen in the superconductor were observed simultaneously. However, in Ref.…”

“…10 An important issue of the coexistence of superconductivity and magnetism from both theoretical [11][12][13][14] and experimental perspectives [15][16][17][18] relates to the microstructure of the magnetic flux, as well as to its dynamics upon variation of the temperature and external magnetic field. Until recently, low temperatures of superconducting and magnetic phase transitions of known single crystals, as well as the requirement of a high spatial resolution, have limited experimental capabilities for visualization of the magnetic flux structure employing e.g.…”

Phase transitions in the domain structure of ferromagnetic superconductors

“…with the maximum value of S N (z) of order of S max N ∼ N 2 at z ∼ 1/πN , M th * , M λ th are given by (21a) and (22), respectively, and N ≈ pl/l v with p given after Eq. (27).…”