title: Development and loss of ferromagnetism controlled by the interplay of Ge concentration and Mn vacancies in structurally modulated Y4Mn(1-x)Ga(12-y)Ge(y).
abstract: The cubic intermetallic phase Y(4)Mn(1-x)Ga(12-y)Ge(y) (x = 0-0.26, y = 0-4.0) has been isolated from a molten gallium flux reaction. It presents a rare example of a system where ferromagnetism can be induced by controlling the vacancies of the magnetic centers. The Y(4)PdGa(12) type crystal structure is made up of a corner-sharing octahedral network of Ga and Ge atoms with Mn atoms at the centers of half the octahedra and Y atoms in the voids. At the highest Ge concentration, y = 4.0, the Mn site is nearly fully occupied, x = 0.05, and the samples are paramagnetic. At a lower Ge concentration, y = 1.0, Mn deficiency develops with x = 0.10. Surprisingly, strong ferromagnetism is observed with T(c) = 223 K. When Ge is excluded, y = 0, Mn is substantially deficient at x = 0.26 and ferromagnetism is maintained with a T(c) of approximately 160 K. In addition, a 6-fold modulated superstructure appears owing to an ordered slab-like segregation of Mn atoms and vacancies. Corresponding bond distortions propagate throughout the octahedral Ga network. Structure-property relationships are examined with X-ray and neutron diffraction, magnetic susceptibility, and electrical resistivity measurements.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Melanie C
authors.initials: MC
authors.lastname: Francisco
authors.forename: Christos D
authors.initials: CD
authors.lastname: Malliakas
authors.forename: Paula M B
authors.initials: PM
authors.lastname: Piccoli
authors.forename: Matthias J
authors.initials: MJ
authors.lastname: Gutmann
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Schultz
authors.forename: Mercouri G
authors.initials: MG
authors.lastname: Kanatzidis