Stabilization of an ambient-pressure collapsed tetragonal phase in CaFe(2)As(2) and tuning of the orthorhombic-antiferromagnetic transition temperature by over 70 K via control of nanoscale precipitates

TitleStabilization of an ambient-pressure collapsed tetragonal phase in CaFe(2)As(2) and tuning of the orthorhombic-antiferromagnetic transition temperature by over 70 K via control of nanoscale precipitates
Publication TypeJournal Article
Year of Publication2011
AuthorsRan S, Bud'ko SL, Pratt DK, Kreyssig A, Kim MG, Kramer MJ, Ryan DH, Rowan-Weetaluktuk WN, Furukawa Y, Roy B, Goldman AI, Canfield PC
Journal TitlePhysical Review B
Volume83
Pages144517
Date Published04
Type of ArticleArticle
ISBN Number1098-0121
Accession NumberWOS:000291975400009
Abstract

We have found a remarkably large response of the transition temperature of CaFe(2)As(2) single crystals grown from excess FeAs to annealing and quenching temperature. Whereas crystals that are annealed at 400 degrees C exhibit a first-order phase transition from a high-temperature tetragonal to a low-temperature orthorhombic and antiferromagnetic state near 170 K, crystals that have been quenched from 960 degrees C exhibit a transition from a high-temperature tetragonal phase to a low-temperature, nonmagnetic, collapsed tetragonal phase below 100 K. By use of temperature-dependent electrical resistivity, magnetic susceptibility, x-ray diffraction, Mossbauer spectroscopy, and nuclear magnetic resonance measurements we have been able to demonstrate that the transition temperature can be reduced in a monotonic fashion by varying the annealing or quenching temperature from 400 degrees to 850 degrees C with the low-temperature state remaining antiferromagnetic for transition temperatures larger than 100 K and becoming collapsed tetragonal, nonmagnetic for transition temperatures below 90 K. This suppression of the orthorhombic-antiferromagnetic phase transition and its ultimate replacement with the collapsed tetragonal, nonmagnetic phase is similar to what has been observed for CaFe(2)As(2) under hydrostatic pressure. Transmission electron microscopy studies indicate that there is a temperature-dependent width of formation of CaFe(2)As(2) with a decreasing amount of excess Fe and As being soluble in the single crystal at lower annealing temperatures. For samples quenched from 960 degrees C there is a fine (of order 10 nm) semiuniform distribution of precipitate that can be associated with an average strain field, whereas for samples annealed at 400 degrees C the excess Fe and As form mesoscopic grains that induce little strain throughout the CaFe(2)As(2) lattice.

DOI10.1103/PhysRevB.83.144517
Alternate JournalPhys. Rev. B