Long-time variation of magnetic structure in multistep metamagnets Ca3(Co-M)2O6

A long-time variation of magnetic structure has been observed in a geometrically frustrated magnet Ca3Co2O6. In order to clarify that the long-time variation in this material does not originate in randomness due to impurities, magnetization measurements have been made on single crystals of diluted compounds Ca-3(Co-M)(2)O-6 (M=Ga, Mg and Al). The longtime variations of the magnetization were detected in these compounds and characteristics of the time variation behavior were not much modified by the introduction of disorder produced by the substitution of non-magnetic atoms. These results show that the long-time variation of the magnetic structure in Ca3Co2O6 is not caused by randomness or imperfections.