title: Incommensurate magnetism in FeAs strips: neutron scattering from CaFe(4)As(3).
abstract: Magnetism in the orthorhombic metal CaFe(4)As(3) was examined through neutron diffraction for powder and single crystalline samples. Incommensurate [q(m) ≈ (0.37-0.39) × b*] and predominantly longitudinally (|| b) modulated order develops through a 2nd order phase transition at TN = 89.63(6) K with a 3D Heisenberg-like critical exponent β = 0.365(6). A 1st order transition at T2 = 25.6(9)  K is associated with the development of a transverse component, locking q(m) to 0.375(2)b*, and increasing the moments from 2.1(1) to 2.2(3)  μ B for Fe2+ and from 1.3(3) to 2.4(4)  μB for Fe+. The ab initio Fermi surface is consistent with a nesting instability in cross-linked FeAs strips.
authors.affiliation: Institute for Quantum Matter and Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Nambu
authors.forename: Liang L
authors.initials: LL
authors.lastname: Zhao
authors.forename: Emilia
authors.initials: E
authors.lastname: Morosan
authors.forename: Kyoo
authors.initials: K
authors.lastname: Kim
authors.forename: Gabriel
authors.initials: G
authors.lastname: Kotliar
authors.forename: Pawel
authors.initials: P
authors.lastname: Zajdel
authors.forename: Mark A
authors.initials: MA
authors.lastname: Green
authors.forename: William
authors.initials: W
authors.lastname: Ratcliff
authors.forename: Jose A
authors.initials: JA
authors.lastname: Rodriguez-Rivera
authors.forename: Collin
authors.initials: C
authors.lastname: Broholm