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.

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We have fabricated a thin film magnetic system consisting of nanoscale Mn11Ge8 ferromagnetic clusters embedded in a MnxGe1−x dilute ferromagnetic semiconductor matrix. The clusters form for growth temperatures of ∼300 °C with an average diameter and spacing of 100 and 150 nm, respectively. While the clusters dominate the magnetic properties, the matrix plays a subtle but interesting role in determining the transport properties. Variable range hopping at low temperatures involves both nanoclusters and MnGe sites, and is accompanied by a negative magnetoresistance attributed in part to spin-dependent scattering analogous to metallic granular systems.

A Group-IV Ferromagnetic Semiconductor: MnxGe 1−x .-Singlecrystal films of the title compound are grown on Ge and GaAs(001) substrates by molecular beam epitaxy. These films have Curie temperatures in the range 25 to 116 K, are p-type semiconductors, and exhibit a pronounced extraordinary Hall effect. Density functional theory calculations 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. The p-type semiconducting character and hole-mediated exchange permit control of ferromagnetic order through application of a gate voltage. -(PARK, Y. D.; HANBICKI, A. T.; ERWIN, S. C.; HELLBERG, C. S.; SULLIVAN, J. M.; MATTSON, J. E.; AMBROSE, T. F.; WILSON, A.; SPANOS, G.; JONKER, B. T.; Science (Washington, D.

An epitaxial orientation of Fe/Cr superlattices -Fe/Cr(211) on MgO(110)is grown by magnetron sputtering.Its structural and magnetic characterizations are presented and compared to those for Fe/Cr(100) superlattices grown simultaneously onto MgO(100) substrates. The epitaxial orientation of the Fe/Cr (211) superlattices is Fe/Cr[011]~iMgO[001] and Fe/Cr[111]iiMgO[110], while that for Fe/Cr(100) is Fe/Cr[001]~~MgO[011]. A uniaxial, in-plane surface anisotropy for the Fe/Cr(211) superlattices along the Fe[011]of 0.06 erg/cm2 is obtained from analysis of the magnetization hysteresis loops.Four oscillations in the antiferromagnetic interlayer coupling and giant magnetoresistance (CiMR) are 0 observed with a period of 18 A for both orientations. The strength, oscillation period, and phase of the magnetic coupling are identical for the two orientations. The GMR values increase by a factor of -4 to 5 on cooling from room temperature to 4.2 K. At 4.2 K the maximum GMR value of the [Fe(14 A)/Cr(8 A)],0 superlattice is 70% for the (211) orientation and 150% for the (100) orientation.