Kavli Affiliate: N. C. Yeh
| First 5 Authors: Zhenjie Feng, Xunqing Yin, Yiming Cao, Xianglian Peng, Tian Gao
| Summary:
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.
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