Absence of magnetic order in (Ba, K)BiO₃

Abstract

The recent discovery of superconductivity in the three-dimensional perovskite system (Ba, K)BiO₃ has added a new group of compounds to the family of high-transition-temperature (high-T _c) superconductors. (Ba, K)BiO₃ contains a three-dimensional BiO network rather than the CuO planes found in two-dimensional high-T _c systems such as YBa₂Cu₃O₇, (La_1.85Sr_0.15)CuO₄, Bi-Ca-Sr-Cu-O and Tl-Ba-Ca-Cu-O. There are, however, a few key features shared by (Ba, K)BiO₃ and the two-dimensional systems; for example the parent compounds BaBiO₃ and La₂CuO₄ both have one valence electron per Bi (or Cu) and doping by K (or Sr) introduces holes into the system as charge carriers. To explore the possible effects of magnetism in the (Ba, K)BiO₃ system and its related compounds, we have performed muon spin rotation (μ SR) experiments on BaBiO₃, (Ba, K)BiO₃ and Ba(Bi_0.9Pb_0.1)O₃, the latter being a member of another oxide superconductor system, Ba(Pb, Bi)O₃ (ref. 3), to search for static magnetic order. In the present study, no signature of magnetic order was found in any of the above systems above T = 10 K. This is in sharp contrast to the two-dimensional systems, where static magnetic order appears in the vicinity of superconductivity.