The A-site ordered manganese perovskite and its colossal magnetoresistance

The A-site ordered manganites show the charge/orbital order (CO) transition far above room temperature. By using this advantage, we have engaged in the realization of colossal magnetoresistance (CMR) at room temperature by introducing some sophisticated disorders to SmBaMn₂O₆. The inter-site disorder of Sm/Ba results in no significant magnetoresistance (MR) effect. The La-substitution for both Sm- and Ba-sites is effective to realize MR effect. At room temperature and 9 T, we have achieved the record of MR effect about 340% in the sintered Sm_0.90La_0.24Ba_0.86Mn₂O₆. In a single crystal of the compound, the perfect CO insulator to ferromagnetic metal (FM) transition is observed at 9 T, showing the room temperature CMR over 1000%. TEM study reveals that the formation of microdomains with CO and FM or magnetic glassy states is crucial for CMR.