Neutron investigation of the magnetic scattering in an iron-based ferromagnetic superconductor

Abstract

Neutron diffraction and small angle scattering experiments have been carried out on the doubleisotopic polycrystalline sample ( 7 Li 0.82 Fe 0.18 OD)FeSe. Profile refinements of the diffraction data establish the composition and reveal an essentially single phase material with lattice parameters of a= 3.7827 Å and c= 9.1277 Å at 4 K, in the ferromagnetic-superconductor regime, with a bulk superconducting transition of T C = 18 K. Small angle neutron scattering (SANS) measurements in zero applied field reveal the onset of ferromagnetic order below T F ≈ 12.5 K, with a wave vector and temperature dependence consistent with an inhomogeneous ferromagnet of spontaneous vortices or domains in a mixed state. No oscillatory long range ordered magnetic state is observed. Field dependent measurements establish a separate component of magnetic scattering from the vortex lattice, which occurs at the expected wave vector. The temperature dependence of the vortex scattering does not indicate any contribution from the ferromagnetism, consistent with diffraction data that indicate that the ordered ferromagnetic moment is quite small. PACS: 74.70.Xa, 74.25.Ha, 75.25.Uv; 75.25.-j *corresponding author. Jeffrey.Lynn@nist.gov 2 The magnetic properties of superconductors have a rich and interesting history. Early work showed that even tiny concentrations of magnetic impurities destroyed the superconducting pairing through the exchange-driven spin depairing mechanism, prohibiting any possibility of cooperative magnetic behavior.[1] The first exception to this rule was provided by the cubic rare-earth substituted CeRu 2 alloys [2][3][4], while the ternary Chevrel-phase (and related) superconductors (e.g. RMo 6 S 8 , R=rare earth) provided the first demonstrations of long range magnetic order coexisting with superconductivity. [5,6] The magnetic ordering temperatures were all quite low (~1 K), where electromagnetic (dipolar + London penetration depth) interactions play a dominate role in the energetics of the magnetic system. The vast majority of these materials order antiferromagnetically where coexistence of long range order with superconductivity was common, but these materials also provided the first examples of the rare occurrence of ferromagnetism and consequent competition with superconductivity in ErRh 4 B 4 , [7][8][9][10] HoMo 6 S 8 , [11][12][13] and HoMo 6 Se 8 .[14] Antiferromagnetic order is found for all the rare earths in the cuprates, which exhibit similar low ordering temperatures. [15] In the borocarbide superconductors again of all the magnetic order is antiferromagnetic, [16] with the singular exception of ErNi 2 B 2 C at low temperature [17,18] where a net magnetization developed that resulted in the spontaneous formation of flux quanta (vortices). [19,20] For the high-T C superconductors of direct interest here, there have been no ferromagnets in either the cuprate or iron-based systems, [15,[21][22][23] [28] For this latter system T C can be as high as 43 K, together with the development of magnetic ord...

Electronic structure of FeSe monolayer superconductors

“…This conclusion was confirmed indirectly in Ref. [40] by observing the scattering of neutrons [39,40].…”

Long-range magnetic order in hydroxide-layer-doped (Li1−x−yFexMnyOD)FeSe

“…Refinements with PXRD were limited to occupation of total transition metal (M * ) doping in the hydroxide layer as well as total transition metal in the FeSe layer yielding a formula: (Li 1−x M * x OD)M y Se. Rietveld refinements of the powder x-ray diffraction yielded a composition of (Li 0.875(2) M * 0.125(2) OD)M Se with lattice parameters a = 3.8008(1)Å and c = 9.2394(2)Å which is in close agreement with previous works 3,4,11,41 .…”

Superconductivity and magnetism in iron sulfides intercalated by metal hydroxides

“…In the similar selenides (Li 1– x Fe x OH)FeSe, which have a T c near 42 K, magnetic ordering in the superconducting state takes place near 10 K due to the iron substituted for lithium in the hydroxide layer. 23,24,28 Seemingly, a magnetic signal proximate to the T c of the (Li 1– x Fe x OH)FeS makes it difficult to evaluate the superconducting properties from heat capacity measurements.…”