Mn-doping induced ferromagnetism and enhanced superconductivity in Bi_4-x Mn_x O_4 S_3 (0.075 < = x < = 0.15)

TL;DR

This study shows that Mn-doping in Bi_4O_4S_3 induces both ferromagnetism and enhanced superconductivity, with a record T_c of 15 K, revealing new pathways to improve BiS_2-based superconductor performance.

Contribution

It demonstrates that Mn-doping induces coexistence of ferromagnetism and superconductivity and enhances T_c in Bi_4O_4S_3, providing insights into doping strategies for higher T_c.

Findings

Mn-doping induces ferromagnetism and enhances T_c up to 15 K.

Excess electron transfer from Mn4+/Mn3+ increases carrier density.

Co and Ni doping do not enhance T_c due to lack of 4+ valence states.

Abstract

We demonstrate that Mn-doping in the layered sulfides Bi_4O_4S_3 leads to stable Bi_4-x Mn_x O_4 S_3 compounds that exhibit both long-range ferromagnetism and enhanced superconductivity for 0.075 < = x < = 0.15, with a possible record superconducting transition temperature (T_c) = 15 K among all BiS_2-based superconductors. We conjecture that the coexistence of superconductivity and ferromagnetism may be attributed to Mn-doping in the spacer Bi2O2 layers away from the superconducting BiS_2 layers, whereas the enhancement of T_c may be due to excess electron transfer to BiS_2 from the Mn4+/Mn3+-substitutions in Bi_2O_2. This notion is empirically corroborated by the increased electron-carrier densities upon Mn doping, and by further studies of the Bi_4-x A_x O_4 S_3 compounds (A = Co, Ni; x = 0.1, 0.125), where the T_c values remain comparable to that of the undoped Bi_4O_4S_3 system (= 4.5 K) due to lack of 4+ valences in either Co or Ni ions for excess electron transfer to the BiS_2 layers. These findings therefore shed new light on feasible pathways to enhance the T_c values of BiS_2-based superconductors.