Macroscopic phase separation of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2−x Se x revealed by μSR

• Published in: Scientific reports Vol. 7; no. 1; pp. 1 - 7
• Main Authors: Nikitin, A. M., Grinenko, V., Sarkar, R., Orain, J.-C., Salis, M. V., Henke, J., Huang, Y. K., Klauss, H.-H., Amato, A., Visser, A. de
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 12-12-2017
• Subjects: Coexistence; Field tests; Magnetism
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-17637-y

Abstract
The compound Sr
0.5
Ce
0.5
FBiS
2
belongs to the intensively studied family of layered BiS
2
superconductors. It attracts special attention because superconductivity at
T
sc
 = 2.8 K was found to coexist with local-moment ferromagnetic order with a Curie temperature
T
C
 = 7.5 K. Recently it was reported that upon replacing S by Se
T
C
drops and ferromagnetism becomes of an itinerant nature. At the same time
T
sc
increases and it was argued superconductivity coexists with itinerant ferromagnetism. Here we report a muon spin rotation and relaxation study (μSR) conducted to investigate the coexistence of superconductivity and ferromagnetic order in Sr
0.5
Ce
0.5
FBiS
2−
x
Se
x
with
x
 = 0.5 and 1.0. By inspecting the muon asymmetry function we find that both phases do not coexist on the microscopic scale, but occupy different sample volumes. For
x
 = 0.5 and
x
 = 1.0 we find a ferromagnetic volume fraction of ~8 % and ~30 % at
T
 = 0.25 K, well below
T
C
 = 3.4 K and
T
C
 = 3.3 K, respectively. For x = 1.0 (
T
sc
 = 2.9 K) the superconducting phase occupies most (~64 %) of the remaining sample volume, as shown by transverse field experiments that probe the Gaussian damping due to the vortex lattice. We conclude ferromagnetism and superconductivity are macroscopically phase separated.