1 / 11

Ferromagnetic Quantum Dots on Semiconductor Nanowires

Ferromagnetic Quantum Dots on Semiconductor Nanowires. Rouin Farshchi EE235 3/7/07. D. G. Ramlan et. al., Nano Letters 6, 50-54 (2006). 1. Spintronics. GMR heads in hard-drives (IBM). Two key requirements: 1- Injection of spin-polarized current 2- Room temperature operation.

savea
Download Presentation

Ferromagnetic Quantum Dots on Semiconductor Nanowires

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Ferromagnetic Quantum Dots onSemiconductor Nanowires Rouin Farshchi EE235 3/7/07 D. G. Ramlan et. al., Nano Letters 6, 50-54 (2006) 1

  2. Spintronics GMR heads in hard-drives (IBM) Two key requirements: 1- Injection of spin-polarized current 2- Room temperature operation 7.9mm x 10mm 16 Mb MRAM chip, IBM GMR Read Heads: C. Tsang. Zhu et. al., IEEE Trans. Magn. 30 3801 (1994) Reviews: S. Wolf et. al., Science 294 1488 (2001) S. Wolf et. al., IBM J. Res & Dev. 50 102 (2006) 2

  3. FM/SC Spin-injection Spin-injection into SC would allow for Gate manipulation of spins  spin transistors Spin injection efficiency: ~P Inject spin-polarized electrons from FM into n-type GaAs and allow recombination with holes from p-type GaAs in LED structure. Measure degree of circular polarization of electroluminescence. P = (I+ - I-) / (I+ + I-) • For Fe as FM: P ~ 2% [1] • Fe is known to form a magnetically • dead layer at GaAs interface [2]. [1] H. J. Zhu et. al., PRL 87 016601 (2001) [2] Y. B. Xu et. al., PRB 58 890 (1998) 3

  4. MnAs on III-V’s Desirable properties of MnAs grown on III-As films: 1- MnAs is ferromagnetic at room temperature 2- Forms a chemically stable interface. 3- Can be grown epitaxially (MBE, MOCVD) on GaAs despite 30% lattice mismatch 4 A. K. Das et. al., PRL 91 087203 (2003)

  5. MnAs dots Epitaxially grown MnAs dots on sulfur passivated GaAs: Low surface energy due to passivation leads to nanoscale MnAs dots with zinc-blend structure  Dot formation relaxes lattice mismatch to 0.7%  Exhibit near room temp TC. 5 K. Ono et. al., JAP 91, 8088 (2002)

  6. MnAs QD’s on InAs NW’s • MnAs quantum dots on InAs nanowires: • InAs Nanowire growth: • -Au catalyst nanoparticles deposited • on Si(100) substrate • -Nanowire growth occurs in MOCVD chamber • under flow of AsH3 at a rate of 6.13 mmole/min, • TMIn at a rate of 1.07 mmole/min, and H2 at 400C • MnAs Quantum dot growth: • -TMIn flow is stopped, T increases to 480C, while • flowing AsH3 and H2. • MnAs QD formation is initiated by introducing • TCMn at a rate of 0.28 mmole/min and increasing • AsH3 flow-rate to 25.42 mmole/min. 100 nm • MnAs QD formation driven by large (~20%) lattice mismatch between MnAs and InAs. Mn is a mobile species on InAs nanowire, facilitating qrowth of strain-relieving 3D islands (Volmer-Weber growth) 6 D. G. Ramlan et. al., Nano Letters 6, 50-54 (2006)

  7. TEM • -InAs NW can be indexed to hexagonal structure, • with lattice spacing d0002 = 3.50 A. • -MnAs QD can be indexed to hexagonal structure • (a-MnAs) with lattice spacing d0002 = 2.86 A, • representing 18% lattice mismatch in [0001] • Hexagonal form of MnAs stabilized, so expect QD’s to be ferromagnetic at room T. 7 D. G. Ramlan et. al., Nano Letters 6, 50-54 (2006)

  8. MFM-magnetic switching Can QD’s acts as nano-bits? -AFM scan locates MnAs QD -MFM cantiliver operating in tapping mode experiences phase shift due to force gradients of magnetic field from QD -MnAs QD’s are known to have small coercivities. QD is stable when subjected to H=40 Oe in direction opposite to remnant magnetization QD magnetization “switches” when applied field is increased to H=60 Oe.  Switching of QD between two stable states Images are 400 x 185 nm2 8 D. G. Ramlan et. al., Nano Letters 6, 50-54 (2006)

  9. MFM-Curie Temperature • Variable temp MFM for determination of TC: • -constant phase contrast up to 308 K (b,c) • -phase contrast disappears abruptly at 313 K • TC lies between 308-313 K, in good agreement with bulk a-MnAs (TC=318 K). Images are 300 x 300 nm2 9 D. G. Ramlan et. al., Nano Letters 6, 50-54 (2006)

  10. Conclusions • MnAs grown on GaAs is a promising FM/SC structure for spin-injection and • has been incorporated into spintronic devices such as spin-valves[1]. • MnAs QD’s grown on InAs NW’s represent a new FM/SC structure with • possible application in high-density memory storage. • Spin-Injection studies from MnAs QD’s into InAs NW’s would be required to • determine their potential for use nano-scale spintronic devices. 10 D. Saha et. al., APL 89, 142504 (2006)

  11. thank you Rouin Farshchi ee235, 3/7/07

More Related