Competing magnetic phases and itinerant magnetic frustration in SrCo2As2

Abstract

Whereas magnetic frustration is typically associated with local-moment magnets in special geometric arrangements, here we show that SrCo2As2 is a candidate for frustrated itinerant magnetism. Using inelastic neutron scattering (INS), we find that antiferromagnetic (AF) spin fluctuations develop in the square Co layers of SrCo2As2 below T ≈ 100 K centered at the stripe-type AF propagation vector of ( 1 2 , 1 2 ), and that their development is concomitant with a suppression of the uniform magnetic susceptibility determined via magnetization measurements. We interpret this switch in spectral weight as signaling a temperature-induced crossover from an instability towards FM ordering to an instability towards stripe-type AF ordering on cooling, and show results from Monte-Carlo simulations for a J1-J2 Heisenberg model that illustrate how the crossover develops as a function of the frustration ratio −J1/(2J2). By putting our INS data on an absolute scale, we quantitatively compare them and our magnetization data to exact-diagonalization calculations for the J1-J2 model [N. Shannon et al., Eur. Phys. J. B 38, 599 (2004)], and show that the calculations predict a lower level of magnetic frustration than indicated by experiment. We trace this discrepancy to the large energy scale of the fluctuations (Javg 75 meV), which, in addition to the steep dispersion, is more characteristic of itinerant magnetism. arXiv:1907.08718v1 [cond-mat.str-el]

Helical magnetic ordering in Sr(Co1−xNix)2As2

“…Here, we study the Ni-doped compounds using neutron and high-energy x-ray diffraction to determine the microscopic details of the AF ground state. Rather than the stripe-AF order one may expect from the spin-fluctuation spectrum of SrCo 2 As 2 [24,25,34], we find that the series develops incommensurate AF order consisting of FM-aligned transition-metal layers where the in-plane ordered magnetic moment (μ ⊥ c) forms a helix propagating perpendicular to the layers (i.e., along c). These results support recent evidence that SrCo 2 As 2 possesses frustrated magnetic interactions driven by flat-band instabilities that place the system on the border between itinerant two-dimensional FM (2D-FM) and stripe-AF [24,34].…”

“…Rather than the stripe-AF order one may expect from the spin-fluctuation spectrum of SrCo 2 As 2 [24,25,34], we find that the series develops incommensurate AF order consisting of FM-aligned transition-metal layers where the in-plane ordered magnetic moment (μ ⊥ c) forms a helix propagating perpendicular to the layers (i.e., along c). These results support recent evidence that SrCo 2 As 2 possesses frustrated magnetic interactions driven by flat-band instabilities that place the system on the border between itinerant two-dimensional FM (2D-FM) and stripe-AF [24,34]. Far more subtle, compositiondependent variations in interlayer interactions and magnetic anisotropy, as recently observed in Sr 1−x Ca x Co 2 As 2 , are at play in determining the details of the layer stacking (such as helical, A-type, or more complex collinear magnetic order) [27].…”

“…[32]. Whereas no AF order is found for x = 0 down to T = 50 mK [34], magnetization and electronic-transport data indicate that small amounts of Ni doping trigger AF order. The dome of AF order spans x ≈ 0.013-0.25 with a maximum Néel temperature of T N ≈ 27 K. We performed neutron and x-ray diffraction on x = 0.06(1) and 0.15(2) single-crystal samples with T N = 20 and 25 K, respectively, as shown in Fig.…”

“…Connections between the unique itinerant magnetic frustration and novel spin fluctuations in cobalt arsenides to partially flat electronic bands have recently been made using densityfunctional-theory calculations, angle-resolved photoemission spectroscopy, and elastic and inelastic neutron-scattering experiments [27,28,[32][33][34]. The flat bands originate from the transition metals' 3d x 2 −y 2 orbitals [28,32] and form a sharp peak in the electronic density of states (DOS) close to E F .…”

Ferromagnetic cluster-glass phase in Ca(Co1−xIrx)2−yAs2Pakhira1, Sangeetha2, Smetana3 et al. 2020Phys. Rev. BSelf Cite14062View full textAdd to dashboardCite

“…On the other hand, SrCo 2 As 2 crystallizes in the ucT structure and CaCo 2−y As 2 crystallizes in the cT structure [14,16,[23][24][25]. Metallic SrCo 2 As 2 is a Stoner-enhanced paramagnet with no long-range magnetic ordering or SC at temperatures above 0.05 K [26]. Inelastic neutron-scattering measurements revealed the presence of stripe-type AFM fluctuations at the same wave vector as observed for the high-T c parent compounds AFe 2 As 2 [26,27].…”