Unusual impurity effect on room-temperature ferromagnet Sr3YCo4O10.56

Abstract We have prepared polycrystalline samples of Sr 3 YCo 4 O 10.56 , Sr 2.4 Ca 0.6 YCo 4 O 10.54 , and Sr 3 YCo 3.76 Mn 0.24 O 10.59 , and found that these materials show unusual impurity effects on their transport and magnetic properties. A tiny amount of impurities such as Mn or Ca suppresses room-temperature ferromagnetism of Sr 3 YCo 4 O 10.56 . With the suppression, their resistivities and thermopowers are also dramatically changed. We propose that the unusual impurity effects are caused by the suppression of orbital ordering.