title: A group-IV ferromagnetic semiconductor: MnxGe1-x.
abstract: We report on the epitaxial growth of a group-IV ferromagnetic semiconductor, Mn(x)Ge(1-x), in which the Curie temperature is found to increase linearly with manganese (Mn) concentration from 25 to 116 kelvin. The p-type semiconducting character and hole-mediated exchange permit control of ferromagnetic order through application of a +/-0.5-volt gate voltage, a value compatible with present microelectronic technology. Total-energy calculations within density-functional theory show that the magnetically ordered phase arises from a long-range ferromagnetic interaction that dominates a short-range antiferromagnetic interaction. Calculated spin interactions and percolation theory predict transition temperatures larger than measured, consistent with the observed suppression of magnetically active Mn atoms and hole concentration.
authors.affiliation: Naval Research Laboratory, Washington, DC 20375, USA.
authors.forename: Y D
authors.initials: YD
authors.lastname: Park
authors.forename: A T
authors.initials: AT
authors.lastname: Hanbicki
authors.forename: S C
authors.initials: SC
authors.lastname: Erwin
authors.forename: C S
authors.initials: CS
authors.lastname: Hellberg
authors.forename: J M
authors.initials: JM
authors.lastname: Sullivan
authors.forename: J E
authors.initials: JE
authors.lastname: Mattson
authors.forename: T F
authors.initials: TF
authors.lastname: Ambrose
authors.forename: A
authors.initials: A
authors.lastname: Wilson
authors.forename: G
authors.initials: G
authors.lastname: Spanos
authors.forename: B T
authors.initials: BT
authors.lastname: Jonker