Crystal chemistry and magnetic properties of manganese zinc alloy “YMn2Zn20” comprising a Mn pyrochlore lattice

The chemical composition, crystal structure, and magnetic properties of a manganese zinc alloy with an ideal composition of YMn2Zn20, which comprises a pyrochlore lattice made of Mn atoms, are reported. The compound is stable only when In or Al is partially substituted for Zn. We have determined the actual chemical formula as YMn2+δZn20−x−δMxYMn2+δZn20−x−δMx, with M=In or Al, and have identified the characteristic preferences with which the incorporated M   and excess MnδMnδ atoms occupy the three crystallographic sites for Zn atoms. The Mn atoms in the pyrochlore lattice possess small magnetic moments that interact with each other antiferromagnetically but exhibit no long-range order above 0.4 K, probably owing to the geometrical frustration of the pyrochlore lattice. As a result, the effective mass of the conduction electrons is considerably enhanced, as observed in the related pyrochlore-lattice compounds (Y,Sc)Mn2 and LiV2O4. However, the presence of excess Mn atoms with large localized magnetic moments comparable to spin 5/2 tends to mask the inherent magnetism of the pyrochlore Mn atoms. It is suggested that “YMn2Zn18In2” with neither excess Mn atoms nor site disorder would be an ideal compound for further study.

Crystal structure of “YMn2Zn18In2”.Figure optionsDownload as PowerPoint slideHighlights
► Two kinds of Mn atoms, pyrochlore Mn and excess Mn, are present in “YMn2Zn20”.
► The excess Mn atom has a large localized moment comparable to that of spin 5/2.
► The small moment on the pyrochlore Mn may give rise to a heavy-fermion-like behavior.
► YMn2Zn18In2 must be an ideal compound with neither excess Mn nor site disorder.