Observation of an anomalous peak in isofield M(T) curves in BaFe2(As0.68P0.32)2 suggesting a phase transition in the irreversible regime

• Published in: Superconductor science & technology 2015-05, Vol.28 (5)
• Main Authors: S Salem-Sugui Jr, Mosqueira, J, Alvarenga, A D, Sóñora, D, Herculano, E P, Hu, Ding, Chen, Genfu, Luo, Huiqian
• Format: Article
• Language: English
• Subjects: As; BaFe; flux creep relaxation rate; second magnetization peak
• ISSN: 0953-2048; 1361-6668
• DOI: 10.1088/0953-2048/28/5/055017

We measure magnetization as a function of temperature, magnetic field, and time in a BaFe2(As0.68P0.32)2 single crystal with Tc = 27.6 K. The fish tail observed in many M(H) curves is used to construct isofield M(T) curves which show an anomalous peak at some temperature Tt, suggesting a possible phase transition in the irreversible regime. A vortex dynamics study performed along the peaks evidences a minimum in the relaxation rate occurring at the same position Tt of the minimum value of M in these peaks. A vortex dynamics study performed on M(H) curves shows two distinct minima in the relaxation rate: a first minimum (H1) for a lower field correlated with Tt and a second (H2) correlated with the peak in the fish tail. A phase diagram is constructed, and the line corresponding to the Tt and H1 points obeys an expression developed in the literature for a structural rhombic to square lattice phase transition, further supporting this view.