Impurity effects on spin dynamics in magnetic and superconducting iron pnictides and chalcogenides

Abstract

In this article, we summarize the effects of magnetic and nonmagnetic impurities on the spin dynamics in Fe‐based superconductors and their parent compounds. The effects of chemical substitution, vacancies, and disorder on the suppression or stabilization of superconductivity and spin‐density‐wave phases are reviewed in the context of recent neutron‐spectroscopy measurements of spin excitations. We also present new results on the structure of magnetic fluctuations in BaFe2As2 single crystals doped with Mn local moments and discuss them in relationship to the previously reported false(π,πfalse) branch of checkerboard magnetic excitations.

Doping effects of Cr on the physical properties of BaFe1.9−xNi0.1CrxAs2

“…Since the effective charge carrier in the parent compound BaFe 2 As 2 already is electron-like 63 , the Cr doping, even it would be naively thought to be hole doping, does not have exactly opposite behaviors comparing to the electron doping from Ni due to particle-hole asymmetry 64 . Moreover, the impurity scattering from the ionic substitution may be quite different between Cr and Ni 9,65 . In this case of BaFe 1.9−x Ni 0.1 Cr x As 2 , a smeared band structure and hole-like Fermi surfaces are then expected.…”

“…Understanding the nature of magnetism is therefore one of the most important issues to reveal the mechanism of superconductivity in these fascinating materials. In one of the typical parent compounds, BaFe 2 As 2 , a stripe type AF order with co-linear structure is formed, where the magnetic moments are aligned along orthorhombic a-axes at low temperature ( Fig.1(c)) [6][7][8][9] . For the electron doped BaFe 2−x T M x As 2 (T M = Ni or Co) system, the long-ranged AF order changes to a short-ranged incommensurate magnetic order and disappears at a finite temperature just before reaching the optimal superconductivity [10][11][12][13][14][15][16][17][18][19][20][21] .…”

Neutron scattering studies on the magnetic interaction in iron-based superconductor BaFe<sub>2</sub><sub>−</sub><sub><italic>x</italic></sub>Ni<sub><italic>x</italic></sub>As<sub>2</sub>

“…总的来说, BaFe 2−x Ni x As 2 体系具有非常丰富的物 性, 多种自由度之间互相耦合, 形成了复杂的相变和 物理行为 [63,64] . 如自旋和晶格的耦合及其与超导的 落谱存在系统演化行为等 [47] .…”

Fast recovery of the pristine magnetic and structural phases in superconducting LaFeAsO0.89F0.11 by Mn/Fe substitution

“…The study of the effect of impurities in superconductors is relevant both in view of their technological applications [1][2][3] as well as for the understanding of the microscopic mechanisms driving superconductivity [4][5][6][7][8][9] . On one hand, impurities act as pinning centers and their presence is necessary for many devices.…”