Superconductivity and ferromagnetism in BM₅Se₉(B = Al, Ga, Ge, Sn, Sb; M = V, Nb, Ta)

The BM5Se9 phases: studies of the behaviour of superconductors and ferromagnets

“…Se 9 , SbNb 5 Se 9 Ga 0.84 Sn 0.15 Nb 5 Se 9 etc [2,3]. without any V atoms, the AC and DC susceptibilities being in good agreement.…”

“…Using different A15/MSe 2 (or A 3 B/MSe 2 ) couples, have been therefore explored several (B/B')(M/A) 5 Se 9 systems where {A=M= (Nb, V, Ta); B=B'= (Al, Ge, Ga, Sn, Sb)}, according to the process which lead to get SnNb 5 Se 9 . It was shown [2,3] that the presence of Vanadium plays a determinant role in the physical properties: as in 1T-VSe 2 where V excess causes a weak paramagnetism [4], in phases with vanadium, couplings are ferromagnet ones, but phases without any V are superconductors: for examples, as SnNb 0.5 Ta 4.5 Se 9 and SnNb 5 Se 9 themselves, GaNb 5 Se 9 , Ga 0.84 Sn 0.15 Nb 5 Se 9 are superconductor but, as GaV 5 Se 9 itself, GaV 0.15 Ta 4.85 Se 9 and Sn 0.94 Ga 0.05 Nb 4.70 V 0.30 Se 9 are ferromagnet [2,3]. So when some vanadium atoms enter in the frame, electronic repulsions appear which destroy the supercon-ductivity state and replace it by ferromagnetic couplings.…”

“…1 Introduction As electronic instabilities in 2H-MSe 2 could lead to a CDW distortion or present an incommensurate ICDW followed by a commensurate CDW, new derivatives were tested and obtained whose properties are a result of a synergy between those of these diselenides and those of the A15 starting compounds. Syntheses performed in the Nb 3 Sn /NbSe 2 and V 3 Ga/VSe 2 systems resulted in the obtention of a superconductor SnNb 5 Se 9 and a ferromagnet GaV 5 Se 9 [1]: the role played by the MSe 2 network used has appeared as a determinant factor [2]. Using different A15/MSe 2 (or A 3 B/MSe 2 ) couples, have been therefore explored several (B/B')(M/A) 5 Se 9 systems where {A=M= (Nb, V, Ta); B=B'= (Al, Ge, Ga, Sn, Sb)}, according to the process which lead to get SnNb 5 Se 9 .…”

“…3 Magnetic results 1) For SnNb 5 Se 9 it was shown that the speed of the quench influences the superconducting volume [2,3], and the major result from the crystal study was the discovery of significant anisotropy when the applied field is ⊥ or // to c, this anisotropy being smaller than that observed in the pristine derivates. Another important result is that SnNb 5 Se 9 could be obtained with the same crystallographic order but without any superconducting behaviour.…”