NMR study of the new magnetic superconductor CaK(Fe0.951Ni0.049)4As4 : Microscopic coexistence of the he

Abstract

The coexistence of a new-type antiferromagnetic (AFM) state, the so-called hedgehog spin-vortex crystal (SVC), and superconductivity (SC) is evidenced by an 75 As nuclear magnetic resonance study on singlecrystalline CaK ( Fe 0.951 Ni 0.049 ) 4 As 4 . The hedgehog SVC order is clearly demonstrated by the direct observation of internal magnetic induction along the c axis at the As1 site (close to K) and a zero net internal magnetic induction at the As2 site (close to Ca) below an AFM ordering temperature T N ∼ 52 K. The nuclear spin-lattice relaxation rate 1 / T 1 shows a distinct decrease below T c ∼ 10 K, providing also unambiguous evidence for the microscopic coexistence. Furthermore, based on the analysis of the 1 / T 1 data, the hedgehog SVC-type spin correlations are found to be enhanced below T ∼ 150 K in the paramagnetic state. These results indicate the hedgehog SVC-type spin correlations play an important role for the appearance of SC in the new magnetic superconductor.

Pressure-induced magnetism in the iron-based superconductors AFe2As2 ( A=K , Cs, Rb)

“…Given that in KFe 2 As 2 bulk superconductivity is observed up to at least P 6 GPa [10], we conclude that for P > 1.8 GPa bulk magnetism and bulk superconductivity coexist within the whole sample volume. Note that a similar type of bulk coexistence between the antiferromagnetic order and superconductivity was previously reported for various compounds belonging to the so-called 11 [29][30][31][32][33][34][35], 122 [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51], 1144 [52][53][54][55], and 21311 [56] families of Fe-SCs.…”

Growth, properties and magnetism of CaKFe4As4

“…A hyperfine field is allowed at As1 for hSVC1 and at As2 for hSVC2 (see mM + 3 and mM + 3 , respectively, in Table 6.7). NMR results reveal that only As1 experienced a nonzero hyperfine field, suggesting that M h2 = 0 down to the lowest temperature measured [48,160].…”

Magnetism and its coexistence with superconductivity in CaK(Fe0.949Ni0.051)4As4Khasanov1, Simutis2, Pashkevich3 et al. 2020Phys. Rev. B9250View full textAdd to dashboardCite

“…The magnetism was further identified as the hedgehog spin-vortex-crystal (SVC) order, which is characterized by noncollinear Fe moments featuring an alternating all-in and all-out motif around the As1 sites within the ab planes and antiferromagnetic coupling along the c direction [13,15]. In addition, the interplay of magnetism and superconductivity in CaK(Fe 1−x Ni x ) 4 As 4 was clearly detected in NMR, Mössbauer spectroscopy, and neutron scattering experiments [10][11][12][13][14][15][16]. As both states compete for the same electrons at the Fermi surface, the magnetic order parameter was found to be strongly reduced below T c .…”