|Berend Thomas Jonker
Ferromagnetic semiconductors are an exciting class of materials in which ferromagnetism and semiconducting properties coexist and are intimately connected. These materials combine the key aspects of two dominant technologies: the nonvolatile character inherent in magnetic materials, and the optical and band-gap engineering properties of current semiconductor devices. In addition, they are both lattice-matched and band structure-matched to a host semiconductor family, and open many new opportunities for spintronic device structures. The discovery of ferromagnetism in III-Mn-V compounds such as Ga1-xMnxAs is especially notable, and provides the ingredients for a potential spintronic device technology in the technologically dominant GaAs/AlAs system.
The more recent discovery of single monolayer direct gap semiconductors in the transition metal dichalcogenide (TMD) family, such as MoS2 and WS2, provides exciting new platforms in which to realize magnetic behavior through doping with elements such as Mn or Cr. In addition, theory predicts magnetic order to exist in single monolayer ScX2 (X = O,S,Se,Te) samples and other materials which have yet to be synthesized. Thus the TMD family and other 2D materials beyond graphene offer exciting new opportunities for achieving ferromagnetically ordered semiconducting materials.
Such ferromagnetic semiconductors may serve as either the source of spin polarized carriers (the spin injector) or the semiconducting transport medium. As a class of materials, ferromagnetic semiconductors are in their infancy; a number of issues exist which must be addressed prior to realizing their expected potential. The broader goals of this research are (1) to improve and understand these materials, (2) to develop new ferromagnetic semiconductor compounds based on new hosts such as the TMDs, and (3) to develop efficient electrical spin injection/transport methods and demonstrate proof-of-concept quantum spin devices based on these materials.
Extensive facilities exist for the growth (MBE, CVD) and characterization of these materials, including Raman, photoluminescence, magneto-optic, transport (charge and spin), structural/magnetic (e.g., AFM/MFM, x-ray diffraction, magnetometry) and clean room processing (e-beam and photolithography).
Jonker BT: Large Area Synthesis of Continuous and Uniform MoS2 Monolayer Films on Graphene, Advanced Functional Materials. DOI: 10.1002/adfm.201401511, 2014
Jonker BT: Anomalous temperature-dependent spin-valley polarization in monolayer WS2, Scientific Reports 5: 18885; doi: 10.1038/srep18885, 2015
Jonker BT: Graphene and Monolayer Transition-Metal Dichalcogenides: Properties and Devices, Journal of Material Research JMR-2015-0727.R1; Focus Issue Review Article: Two-Dimensional Heterostructure Materials, 2016
Ferromagnetic; Magnetoelectronics; Quantum spin electronics; Semiconductors; Spin injection; Spin transport; Spintronics;