Flat-band magnetism and helical magnetic order in Ni-doped SrCo2As2

Abstract

A series of Sr(Co1−xNix)2As2 single crystals was synthesized allowing a comprehensive phase diagram with respect to field, temperature, and chemical substitution to be established. Our neutron diffraction experiments revealed a helimagnetic order with magnetic moments ferromagnetically (FM) aligned in the ab plane and a helimagnetic wavevector of q = (0, 0, 0.56) for x = 0.1. The combination of neutron diffraction and angle-resolved photoemission spectroscopy (ARPES) measurements show that the tuning of a flat band with d x 2 −y 2 orbital character drives the helimagnetism and indicates the possibility of a quantum order-by-disorder mechanism.

Non-Fermi-liquid types of behavior associated with a magnetic quantum critical point in Sr(Co1−xNix)2As2Sangeetha1, Wang2, Smirnov3 et al. 2019Phys. Rev. B278430View full textAdd to dashboardCite

“…The above MFT discussion of helical ordering may be expected to be of only qualitative significance, since the MFT was formulated for local-moment AFMs instead of itinerant AFMs. However, magnetic neutron diffraction measurements [63,64] found that the magnetic structure is indeed helical, with helix turn angles that decrease from 104 • to 94 • on increasing x from x = 0.06 to 0.15, which have the same trend and are of the same order as we infer in Fig. 12 from Eq.…”

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

“…CaCo 2 As 2 shows Atype AF order with μ c [30], the occurrence of which is tied to partially flat electronic bands lying closer to the Fermi energy E F than for paramagnetic SrCo 2 As 2 [28]. The value of c changes with x for both Sr(Co 1−x Ni x ) 2 As 2 [32,33] and Sr 1−x Ca x Co 2 As 2 [36], and, interestingly, both series show regions of AF order with μ ⊥ c for ratios of c/a corresponding to their uncollapsed-tetragonal (ucT) phases [32,36]. The ucT phase is characterized by weaker As-As covalent bonding than in the cT phase [37].…”

“…Recently, the electron-doped materials Sr 1−x La x Co 2 As 2 [31] and Sr(Co 1−x Ni x ) 2 As 2 [32,33] have been shown to develop long-range AF order for extremely low substitutions of x ≈ 1% as shown by the magnetic phase diagram in Fig. 1(a) for the Ni-doped series.…”

“…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. B14062View full textAdd to dashboardCite

“…Recently, non-Fermi-liquid types of behavior associated with a composition-induced magnetic quantum-critical point in Sr(Co 1−x Ni x ) 2 As 2 crystals near x = 0.3 has been reported [37]. In addition, crystals of Sr(Co 1−x Ni x ) 2 As 2 with 0 < x < 0.3 exhibit c-axis helical or spin-density-wave AFM ordering [37][38][39], which is quite unusual in itinerant antiferromagnets. A small amount (2.5%) of La doping has been reported to cause FM ordering in Sr 1−x La x Co 2 As 2 [40,41].…”