In the temperature-concentration phase diagram of most iron-based superconductors, antiferromagnetic order is gradually suppressed to zero at a critical point, and a dome of superconductivity forms around that point. The nature of the magnetic phase and its fluctuations is of fundamental importance for elucidating the pairing mechanism. In Ba1-xKxFe2As2 and Ba1-xNaxFe2As2, it has recently become clear that the usual stripelike magnetic phase, of orthorhombic symmetry, gives way to a second magnetic phase, of tetragonal symmetry, near the critical point, in the range from x = 0.24 to x=0.28 for Ba1-xKxFe2As2. In a prior study, an unidentified phase was discovered for x < 0.24 but under applied pressure, whose onset was detected as a sharp anomaly in the resistivity. Here we report measurements of the electrical resistivity of Ba1-xKxFe2As2 under applied hydrostatic pressures up to 2.75 GPa, for x = 0.22, 0.24, and 0.28. The critical pressure above which the unidentified phase appears is seen to decrease with increasing x and vanish at x = 0.24, thereby linking the pressure-induced phase to the tetragonal magnetic phase observed at ambient pressure. In the temperature-concentration phase diagram of Ba1-xKxFe2As2, we find that pressure greatly expands the tetragonal magnetic phase, while the stripelike phase shrinks. This reveals that pressure may be a powerful tuning parameter with which to explore the interplay between magnetism and superconductivity in this material.
E. Hassinger and G. Gredat and F. Valade and S. R. De Cotret and O. Cyr-Choinière and A. Juneau-Fecteau and J. P. Reid and H. Kim and M. A. Tanatar and For full list of authors, see publisher's website., "Expansion of the Tetragonal Magnetic Phase with Pressure in the Iron Arsenide Superconductor Ba₁₋ₓKₓFe₂As₂," Physical Review B, vol. 93, no. 14, article no. 144401, American Physical Society (APS), Apr 2016.
The definitive version is available at https://doi.org/10.1103/PhysRevB.93.144401
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01 Apr 2016