Electronic and magnetic properties of the kagome systems YBaCo4O7 and YBaCo3MO7 (M=Al, Fe)

We present a combined experimental and theoretical x-ray absorption spectroscopy study of the class of cobaltates YBaCo4O7 and YBaCo3MO7 (M=Al, Fe). The focus is on the local electronic and magnetic properties of the transition metal ions in these geometrically frustrated kagomeacute compounds. For the mixed valence cobaltate YBaCo4O7, both the Co2+ and Co3+ are found to be in the high-spin state. The stability of these high-spin states in tetrahedral coordination is compared with those in the more studied case of octahedral coordination. For the compound YBaCo3FeO7, we find exclusively Co2+ and Fe3+ as charge states.