Elshan Akhadov Spin Electronics QuarkNet, June 28, 2002 Peng Xiong Department of Physics and MARTECH Florida State University

Elshan Akhadov Speed: 10 0 Hz Size: m Cost: $10 6 /transistor Speed: 10 9 Hz Size: m Cost: $10 -5 /transistor Moore’s Law… is the end in sight? SOURCEGATEDRAIN MOSFET

Elshan Akhadov Magnetic Information Storage: superparamagnetic limit Density: 2 kb/in 2 Speed: 70 kb/s Size:  ” x 50 Capacity: 5 Mb Density: 20 Gb/in 2 Speed: 200 Mb/s Size:  ” x 2 Capacity: 50 Gb

Elshan Akhadov Superparamagnetic Limit: thermal stability of magnetic media

Elshan Akhadov Semiconductor Random Access Memory: alternatives? High speed Low density High power consumption Volatile M O S

Elshan Akhadov Metal-based Spintronics: Spin valve and magnetic tunnel junction EFEF N(E) E E H R H M EFEF E E H Applications: magnetic sensors, MRAM, NV-logic

Elshan Akhadov Spintronics in Semiconductor: spin transistor Datta and Das, APL, 1990 Issues Spin polarized material Spin injection Spin coherence Spin detection SOURCEDRAIN H H GaAs Dreams High performance opto-electronics Single-chip computer (instant on; low power) Quantum computation GATE

Elshan Akhadov RFRF Schmidt et.al., PRB, 2000 Solutions: Use injector with 100% spin polarization Non-diffusive injection Conductivity matching SC NN NN FM FF FF II II I Spin Injection: the conductivity mismatch R N  RFRF R N 

Elshan Akhadov half-metallic ferromagnet E U ex Measurement of spin polarization: using a superconductor CrO 2 : a half metal T c = 400 K m = 2  B /Cr p = 100% Schwarz, J. Phys. F, 1986 normal metal E metallic ferromagnet E 4s 3d

Elshan Akhadov E N(E)   EFEF Andreev reflection: normal metal/superconductor eV N S Question: What could happen to an electron with energy eV <  when it hits S from N? A. bounce back; B. go into S as an electron; C. go into S in a Cooper pair. 1. A and B 2. B and C 3. C and A 4. A and B and C NS

Elshan Akhadov Andreev reflection: normal metal/superconductor Z = 0 clean metallic contact Z >> 1 tunnel junction Z ~ 1 in-between Blonder, Tinkham, and Klapwijk, PRB, 1982 p = 0

Elshan Akhadov E DOS   EFEF eV F S Andreev reflection: ferromagnet/superconductor p = 75% Z = 0 metallic contact Z ~ 1 in-between Z >> 1 tunnel junction V

Elshan Akhadov p = 75% Z = 0 metallic contact Z ~ 1 in-between Z >> 1 tunnel junction V Z = 0 metallic contact Z >> 1 tunnel junction Z ~ 1 in-between p = 0 Comparison: normal metal and ferromagnet V

Elshan Akhadov Spin Polarization of CrO 2 : our approach Planar junction  real device structure Artificial barrier  controlled interface Preservation of spin polarization at and across barrier Key step: controlled surface modification of CrO 2 via Br etch

Elshan Akhadov Furnace, T=280° C substrate Heater block, T=400°C O 2 flow Cr 8 O 21 precursor CrO 2 Film Growth: Chemical Vapor Deposition Ivanov, Watts, and Lind, JAP, 2001

Elshan Akhadov CrO 2 TiO 2 Pb or Al I  Grow CrO 2 film  Pattern CrO 2 stripe  Surface modification: Br etch  Deposit S cross stripes CrO 2 Pb or Al V ~ Lock-in dV/dI vs V in He4 (1K) or He3 (0.3K) cryostats Junction Fabrication and Measurement

Elshan Akhadov Results: CrO 2 /(I)/Pb junctions Metallic contact Z = 0p = 97% T = 1.2 K  = 1.44 meV T = 400 mK Tunnel junction High quality barrier w/o inelastic scattering

Elshan Akhadov Measurement of spin polarization in high-Z junctions: using Zeeman splitting E N(E)   EFEF eV F S Meservey and Tedrow, Phys. Rep., 1994 eV/  HH H

Elshan Akhadov Al CrO 2 H Al In order to get high H c : Ultrathin S film Parallel field Negligible s-o interaction Zeeman splitting in an F/I/S junction

Elshan Akhadov T =400 mK Results: Zeeman splitting +2.5T -2.5T

Elshan Akhadov Summary (CrO 2 ) Verified half-metallicity of CrO 2 Engineered an artificial barrier on CrO 2 surface Preserved complete spin polarization at interface Achieved full spin injection from a half metal Future Apply the technique to other systems Magnetic tunnel junction

Elshan Akhadov CrO 2 /I/Co magnetic “tunnel” junction H CrO 2 Co AlO x

Elshan Akhadov Jeff Parker Jazcek Braden Steve Watts Pavel Ivanov Stephan von Molnár Pedro Schlottmann David Lind The People

Elshan Akhadov “computers with wires no wider than 100 atoms, a microscope that could view individual atoms, machines that could manipulate atoms 1 by 1, and circuits involving quantized energy levels or the interactions of quantized spins.” Richard Feynman – “There’s Plenty of Room at the Bottom” 1959 APS Meeting Let’s build