New magnetic materials for Spintronics

Transcription

1 ew magnetic materials for Spintronics Juana Moreno utline What is spintronics? And why? Ferromagnetic semiconductors rganic magnets

2 What is spintronics? And why? Spin-unpolarized current: Electrons move with random spin orientation Spin-polarized current: Electrons move with same spin orientation

3 Why spintronics? We need faster, smaller, more efficient chips By 2020 a transistor in a chip may reach the size of a few atoms. Electronics based on a new paradigm is needed!

4 Devices based on static spins Giant magneto-resistance hard-disks GMR effect (1988) IBM hard disk (1997) [Prinz, Science 1998]

5

6 The advantage of using spin. Silicon technology (no equivalent change) 0.1 penny/mb! GMR introduction (advantage of using spin in devices)

7 LB1 Devices based on spin-polarized currents Spin Field Effect Transistor Datta-Das (1990) Spin precession due to spin-orbit interaction with spin-orbit splitting controlled by gate potential p- type n- type Spin LED H split the spin levels circularly polarized light spin injector - Very small spin injections! hν

8 Slide 7 LB1 Rashba interaction is a "zero field splitting" wherein a gradient electric field can rotate the spins in a typical FET, the gate controls the current flow by increasing or decreasing the size of the channel by controlling the size of the p-n depletion region in a spin FET, the gate controls the rotation of spin, where the drain senses the spin direction. For parallel alignment the resistance is low, for antiparallel resistance is higher this method of rotating the spin takes very little energy so these devices are in theory much more efficient than present FET Luigi Batafuco, 10/28/2004

9 Some successes: Electrical control of magnetization H. hno et al., ature (2000) Photogenerated magnetism Koshihara et al. (1997)

10 Difficulties to build spintronic devices? Metal devices don t amplify the current. Mixed devices have problems with spin injection. Large scattering at the interface between ferromagnetic metal-semiconductor due to conductivity mismatch. Metal-semiconductor interface Solution: a magnetic semiconductor as spin-injector Easily integrated with current semiconductor technology Multiple functionality Amplification

11 utline What is spintronics? And why? Ferromagnetic semiconductors rganic magnets Mn Mn

12 H 0 - c J = H Carrier mediated ferromagnetism H = H 0 - J c Σ S. i σ(r i ) R i carrier dispersion Mn spin carrier spin Mn Mn Zener or double-exchange Hamiltonian

13 Weak-coupling mean-field theory [Dietl et al., Science (2000)] T J 2 c c Dietl s theory is too simplistic to analyze material properties. Room temperature

14 T c for carriers with angular momentum j max T c (j) reaches a maximum for j = 3/2! Model for GaAs must include two hole bands (j = 3/2) with light and heavy masses. T c is suppressed due to magnetic frustration. J. M, Fishman & Jarrell, Phys. Rev. Lett. 96,

15 utline What is spintronics? And why? Ferromagnetic semiconductors rganic magnets

16 rganic-based Materials in Spintronics Advantages: smoother interfaces longer spin coherence lengths more flexible metallicity range scaffolding to hold metal centers cheaper bottom-up fabrication low-weight mechanically flexible,... Disadvantages: low conductivity difficult to grow organic + metal low-weight,.

17 TC1 on-magnetic rganics in Spintronics GMR: Xiong et al., ature (2004) LED: Salis et al., Phys. Rev. B (2004) MTJ: Petta et al., Phys. Rev. Lett. (2004) TMR: Santos, Phys. Rev. Lett. (2007)

18 Slide 16 TC1 the first three examples are of GMR (1) giant magneto resistance Alq3 between LSM and cobalt (2) magneto resistance (3) magnetic field dependent electroluminesence spin polarized organic light emitting diode (4) octanedithiol between nickel Center for anoscale Science and Engineering, 6/23/2006

19 Magnetic rganic Semiconductors: Porphyrins & Metalloporphyrins M etalloporphyrin Q. Huo, Langmuir 2004, J. Porphyrins and Phthalocyanines , Fe 3+, Mn 3+, 2+ 2+, 2+ Paramagnetic metal centers Goldberg, Crystal growth & Design, 2004, 2006

20 Metalloporphyrin modeling t 1 t 1 t 2 Majidi, Moreno, Schwalm, Fishman (2007)

21 Majidi, Moreno, Schwalm, Fishman (2007)

22 nclusions Spintronics as a new paradigm for computer technology. eed for new spintronic materials: Dilute magnetic semiconductors rganic magnets

23 Working assets: Unjong Yu (South Korea), Aziz Majidi (Yakarta, Indonesia), Brian Moritz (Standford/SLAC), Peter Reis, Majid li, Karlis Mikelsons (Georgetown), Karan Aryanpour (SUY-Buffalo), Alex Brandt (MSU Moorhead), Mason Swanson (DSU), Randy Fishman (RL), Mark Jarrell (LSU), Paul Kent & Thomas Maier (RL), Mark Hoffmann & Bill Schwalm (UD), Leigh Smith (Cincinnati), Qun Huo (U. Central Florida), Anthony Caruso (U. Missouri, Kansas City), Konstantin Pokhodnya (DSU) Grants: EPS & EPS (DEPSR) 2005 RAU Junior Faculty Award DMR , ISE TeraGrid-CyberInfrastructure Partnership University of orth Dakota mputational Research Center

24 PIRE: Graduate Education and Research in Petascale Many Body Methods for mplex rrelated Systems: A llaboration with Partners in Germany and Switzerland Juana Moreno, Mark Jarrell Louisiana State University Karen Tomko hio Supercomputer Center

25 Participating rganizations In the USA: Louisiana State University University of orth Dakota Hillsdale llege hio Supercomputer Center ak Ridge ational Lab In Germany: Max Planck Institute, Stuttgart University of Gőttingen Technical Universit of Dortmund University of Wűrzburg In Switzerland: ETH, Zűrich J