Research Highlight

Doping strengthens magnetism in an iron-based crystal

Temperature-dependent heat capacity for Ba1-xTlxFe2As2shows an increase in magneto-elastic anomaly at 5%, then the usual drop at 9%. Typical single crystal size is shown in the bottom inset. 

Thallium-doping (5%) of BaFe2As2 crystal causes a surprising rise of the antiferromagnetic transition temperature (TN), related to

Temperature-dependent heat capacity for Ba1-xTlxFe2As2shows an increase in magneto-elastic anomaly at 5%, then the usual drop at 9%. Typical single crystal size is shown in the bottom inset. Temperature-dependent heat capacity for Ba1-xTlxFe2As2shows an increase in magneto-elastic anomaly at 5%, then the usual drop at 9%. Typical single crystal size is shown in the bottom inset.  (hi-res image)
magneto-elastic coupling. This is the first example of the increase of TN with chemical doping in BaFe2As2. Understanding the role of chemical doping for changing magnetism or causing superconductivity can lead to design principles for magnets and superconductors that operate at desired temperatures. 

BaFe2As2 crystals were chemically doped with Tl, for the possibility of creating a similar high-temperature superconductor (Tc = 38 K) found in hole-doped Ba1-xKxFe2As2. However, and unexpectedly, the crystals exhibited highly unusual behavior for which TNfirst increases in 5% chemical substitution, before the expected drop with 9% in Ba1-xTlxFe2As2. Ba1-xTlxFe2As2 behaves differently from the traditionally explored Ba1-xKxFe2As2, due to the differences in structural details upon doping.

This study used a combination of crystal synthesis, temperature-dependent single-crystal X-ray diffraction, ORNL’s neutron diffraction user facility at the High Flux Isotope Reactor, and first principles calculations, as well as characterization of the electrical resistance, magnetic susceptibility, and heat capacity. 

A. S. Sefat, L. Li, H. B. Cao, M. A. McGuire, B. Sales, R. Custelcean, and D. S. Parker, “Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2,” Scientific Reports (2016).  http://dx.doi.org/10.1038/srep21660

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