Ferromagnetic Superconductors: A Vortex Phase in Ternary Rare-Earth Compounds

Kuper, C.G.; Revzen, M.; Ron, A.

doi:10.1103/physrevlett.44.1545

Cited by 119 publications

(30 citation statements)

References 8 publications

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“…Indeed, an attractive long range vortex interaction was predicted under certain assumptions in Ref. 6 in the presence of ferromagnetism. Another interesting consideration is that with a fully developed internal field, the magnetic energy is 2 ϫ 700 G ϫ 7.8 B / k B = 0.7 K / k B per Er atom.…”

Section: Discussionmentioning

confidence: 99%

“…3,4 The second possible form of coexistence is a so-called spontaneous vortex lattice which carries the field generated by the magnetization. 1,5,6 Such a spontaneous vortex lattice has never been observed in a zero-field-cooled sample, but ErNi 2 B 2 C was suggested as a strong candidate. 5 Evidence for the existence of a vortex lattice in ErNi 2 B 2 C after magnetic cycling has been reported 7 based on small-angle neutron scattering ͑SANS͒.…”

Section: Introductionmentioning

confidence: 98%

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Scanning Hall probe imaging ofErNi2B2C

et al. 2006

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We report scanning Hall probe imaging of ErNi 2 B 2 C in the superconducting, antiferromagnetic, and weakly ferromagnetic regimes in magnetic fields up to 20 Oe, well below H c1 , with two results. First, imaging isolated vortices shows that they spontaneously rearrange on cooling through the antiferromagnetic transition temperature T N = 6 K to pin on twin boundaries, forming a striped pattern. Second, a weak, random magnetic signal appears in the ferromagnetic phase below T WFM = 2.3 K, and no spontaneous vortex lattice is present down to 1.9 K. We conclude that ferromagnetism coexists with superconductivity either by forming small ferromagnetic domains or with oscillatory variation of the magnetization on sub-penetration-depth length scales.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Scanning Hall probe imaging ofErNi2B2C

et al. 2006

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“…This scheme was used in studies of rare earth ternary compounds [7,30,31,32]. Alternatively [33], one may use from the beginning the total ferromagnetic free energy f F (a f , M ) as given by Eqs. (6) - (8) …”

Section: Ginzburg-landau Free Energymentioning

confidence: 99%

Meissner phases in spin-triplet ferromagnetic superconductors

Shopova

Uzunov

2005

Phys. Rev. B

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We present new results for the properties of phases and phase transitions in spin-triplet ferromagnetic superconductors. The superconductivity of the mixed phase of coexistence of ferromagnetism and unconventional superconductivity is triggered by the presence of spontaneous magnetization. The mixed phase is stable but the other superconducting phases that usually exist in unconventional superconductors are either unstable or for particular values of the parameters of the theory some of them are metastable at relatively low temperatures in a quite narrow domain of the phase diagram. Phase transitions from the normal phase to the phase of coexistence is of first order while the phase transition from the ferromagnetic phase to the coexistence phase can be either of first or second order depending on the concrete substance. Cooper pair and crystal anisotropies determine a more precise outline of the phase diagram shape and reduce the degeneration of ground states of the system but they do not change drastically phase stability domains and thermodynamic properties of the respective phases. The results are discussed in view of application to metallic ferromagnets as UGe2, ZrZn2, URhGe.

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“…In the SVP the internal magnetic induction is screened locally, vortexby-vortex, so the problem considered by Ginsburg does not apply. Further work on SVPs has included the suggested realization in ErRh 4 B 4 , [3] in Eu x Sn 1−x Mo 6 S 8 , [4] in ErNi 2 B 2 C, [5] and possibly in p-wave systems. [6] A serious impediment to SC arising well within the FM phase is the Zeeman splitting of the carrier bands, which makes the majority and minority Fermi surfaces inequivalent, so the states | k ↑> and | − k ↓> do not both lie on the Fermi surface, and total momentum q ≡ k + k ′ =0 pairs are not available for pairing.…”

mentioning

confidence: 99%

Superconductivity in FerromagneticRuSr2GdCu2O8

1999

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Relying on the inhomogeneous (layered) crystal, electronic, and magnetic structure, we show how superconductivity can coexist with the ferromagnetic phase of RuSr2GdCu2O8 as observed by Tallon and coworkers. Since the Cu d x 2 −y 2 orbitals couple only to apical O px, py orbitals (and only weakly), which also couple only weakly to the magnetic Ru t2g orbitals, there is sufficiently weak exchange splitting, especially of the symmetric CuO2 bilayer Fermi surface, to allow singlet pairing. The exchange splitting is calculated to be large enough that the superconducting order parameter may be of the Fulde-Ferrell-Larkin-Ovchinnikov type. We also note that π-phase formation is preferred by the magnetic characteristics of RuSr2GdCu2O8.The antagonism between ferromagnetism (FM) and singlet superconductivity (SC) was discussed early on by Ginsburg [1]. His simple conclusion, based upon an inverse Meissner effect that would set up surface currents to shield the external region from the frozen-in magnetic field B int = 4πM , was that coexistence was not viable except in samples not much larger that the field penetration depth. Krey showed how to circumvent this restriction [2] by the formation of spiral magnetic order or, in type II superconductors, by the formation of a spontaneous vortex phase (SVP). In the SVP the internal magnetic induction is screened locally, vortexby-vortex, so the problem considered by Ginsburg does not apply. Further work on SVPs has included the suggested realization in ErRh 4 B 4 , [3] in Eu x Sn 1−x Mo 6 S 8 , [4] in ErNi 2 B 2 C, [5] and possibly in p-wave systems. [6] A serious impediment to SC arising well within the FM phase is the Zeeman splitting of the carrier bands, which makes the majority and minority Fermi surfaces inequivalent, so the states | k ↑> and | − k ↓> do not both lie on the Fermi surface, and total momentum q ≡ k + k ′ =0 pairs are not available for pairing. Getting around this difficulty with q =0 pairs in the case of applied fields or dilute magnetic impurities has led to Fulde-Farrell-LarkinOvchinnikov (FFLO) type theories, [7] where either the SC or FM order parameter (or both) develops spatial variation to accommodate the other.Tallon et al. [8,9] have injected new excitement into this question of coexistence of SC and FM by reporting the superconducting ferromagnet RuSr 2 GdCu 2 O 8−δ (Ru1212). This system was first reported by Bauernfiend et al.[10] as superconducting but not magnetic, and other reports [11,12] indicate that properties are dependent on the method of preparation. Unlike almost all previously reported cases of coexisting SC and FM, this material is first magnetic (T M = 132 K, due to ordering of Ru ions with an ordered moment of 1 µ B /Ru) and then becomes SC only well within the FM phase. Superconductivity appears at T S ≈ 35-40 K, and only at 2.6 K do the Gd ions order (antiferromagnetically). The data are reproducible, specific heat data indicate a bulk SC transition, and muon spin rotation experiments indicate the magnetism is homogeneous and is ...

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Ferromagnetic Superconductors: A Vortex Phase in Ternary Rare-Earth Compounds

Cited by 119 publications

References 8 publications

Scanning Hall probe imaging ofErNi2B2C

Scanning Hall probe imaging ofErNi2B2C

Meissner phases in spin-triplet ferromagnetic superconductors

Superconductivity in FerromagneticRuSr2GdCu2O8

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