New magnetic materials for Spintronics Juana Moreno Outline • What is spintronics? And why? • Ferromagnetic semiconductors • Organic magnets
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New magnetic materials for SpintronicsJuana Moreno
Outline• What is spintronics? And why?• Ferromagnetic semiconductors• Organic magnets
What is spintronics? And why?
Spin-unpolarized current:Electrons move with random spin
orientation
Spin-polarized current:Electrons move with same spin
orientation
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!
Devices based on “static” spins
Giant magneto-resistance hard-disksGMR effect (1988)
IBM hard disk (1997)
[Prinz, Science 1998]
http://www.research.ibm.com/research/gmr.html
GMR introduction(advantage of using spin in devices)
Silicon technology(no equivalent change)
The advantage of using spin….
0.1 penny/MB!
Spin Field Effect Transistor
Datta-Das (1990)
Spin precession due to spin-orbit interaction with spin-orbit splitting controlled by gate potential
Devices based on spin-polarized currents
p- type n- typep- type n- type
Spin LEDH split the spin levels circularly polarized light.
+ - spin injector
-
-
++ -- spin injector
-
-
spin injector
--
--
hν
Very small spin injections!
LB1
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-ndepletion 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 FETLuigi Batafuco, 10/28/2004
Electrical control of magnetization
H. Ohno et al., Nature (2000)
Photogeneratedmagnetism
Koshihara et al. (1997)
Some successes:
Large scattering at the interface between ferromagnetic metal-semiconductor due to conductivity mismatch.
• Metal devices don’t amplify the current.
• Mixed devices have problems with spin injection.
Solution: a magnetic semiconductor as spin-injector
• Easily integrated with current semiconductor technology
• Multiple functionality
• Amplification
Metal-semiconductor interface
Difficulties to build spintronic devices?
MnMn
Outline• What is spintronics? And why?• Ferromagnetic semiconductors• Organic magnets
Zener or double-exchange Hamiltonian
MnMn
H = H0 - Jc Σ Si σ(Ri)Ri
.
carrier dispersion Mn spin carrierspin
H = H0 - Jc
Carrier mediated ferromagnetism
Weak-coupling mean-field theory
[Dietl et al., Science (2000)]
Dietl’s theory is too simplistic to
analyze material properties.
2cc JT ∝
Room temperature
Tc (j) reaches a maximum for j = 3/2!
max
J. M, Fishman & Jarrell, Phys. Rev. Lett. 96, 237204
Tc for carriers with angular momentum j
Model for GaAs must include two hole bands (j = 3/2) with light and heavy masses. Tc is suppressed due tomagnetic frustration.
N
N N
NCo
O
O
O O
Ni
Ni
N
N N
NCo
O
O
O O
Ni
Ni
O
O
N
N N
NCo
O
O
O O
Ni
Ni
N
N N
NCo
O
O
O O
Ni
Ni
O
O
O O O O
NiO O
NiO O
NiO
O
NiO
O
Outline• What is spintronics? And why?• Ferromagnetic semiconductors• Organic magnets
Organic-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, ….
N
N N
NCo
O
O
O O
Ni
Ni
N
N N
NCo
O
O
O O
Ni
Ni
O
O
N
N N
NCo
O
O
O O
Ni
Ni
N
N N
NCo
O
O
O O
Ni
Ni
O
O
O O O O
NiO O
NiO O
NiO
O
NiO
O
GMR: Xiong et al., Nature (2004)
OLED: Salis et al., Phys. Rev. B (2004)
MTJ: Petta et al., Phys. Rev. Lett. (2004)
TMR: Santos, Phys. Rev. Lett. (2007)
Non-Magnetic Organics in SpintronicsTC1
Slide 16
TC1 the first three examples are of GMR
(1) giant magneto resistanceAlq3 between LSMO and cobalt
(2) magneto resistance
(3) magnetic field dependent electroluminesencespin polarized organic light emitting diode
(4) octanedithiol between nickelCenter for Nanoscale Science and Engineering, 6/23/2006
Porphyrins & Metalloporphyrins
M etalloporphyrin
N i2+, Fe3+, M n3+,C o2+
N i2+, C o2+
P aram agnetic m etal centers
Magnetic Organic Semiconductors:
Q. Huo, Langmuir 2004, J. Porphyrins and Phthalocyanines 2005
Goldberg, Crystal growth & Design, 2004, 2006
N
N N
NCo
O
O
O O
Ni
Ni
N
N N
NCo
O
O
O O
Ni
Ni
O
O
N
N N
NCo
O
O
O O
Ni
Ni
N
N N
NCo
O
O
O O
Ni
Ni
O
O
O O O O
NiO O
NiO O
NiO
O
NiO
O
Co
Ni
Metalloporphyrin modeling
t1
Majidi, Moreno, Schwalm, Fishman (2007)
t2
t1
Majidi, Moreno, Schwalm, Fishman (2007)
Conclusions• Spintronics as a new paradigm for computer technology.
• Need for new spintronic materials:
• Dilute magnetic semiconductors
• Organic magnets
TeraGrid-CyberInfrastructure Partnership University of North Dakota Computational Research Center
Grants: EPS-0132289 & EPS-0447679 (NDEPSCoR)2005 ORAU Junior Faculty AwardDMR-0548011, OISE-0730290
Working assets: Unjong Yu (South Korea), Aziz Majidi (Yakarta, Indonesia),Brian Moritz (Standford/SLAC),Peter Reis, Majid Nili, Karlis Mikelsons (Georgetown), Karan Aryanpour(SUNY-Buffalo),Alex Brandt (MSU Moorhead), Mason Swanson (NDSU),Randy Fishman (ORNL), Mark Jarrell (LSU), Paul Kent & Thomas Maier (ORNL), Mark Hoffmann & Bill Schwalm (UND),Leigh Smith (Cincinnati), Qun Huo (U. Central Florida), Anthony Caruso (U. Missouri, Kansas City), Konstantin Pokhodnya (NDSU)
PIRE: Graduate Education and Research in Petascale Many Body Methods for Complex
Correlated Systems:A Collaboration with Partners in Germany
and Switzerland
Juana Moreno, Mark JarrellLouisiana State University
Karen TomkoOhio Supercomputer Center
In the USA:Louisiana State UniversityUniversity of North Dakota
Hillsdale CollegeOhio Supercomputer Center
Oak Ridge National Lab
In Germany:Max Planck Institute, Stuttgart
University of GőttingenTechnical Universit of
DortmundUniversity of Wűrzburg
In Switzerland:ETH, Zűrich
J
Participating Organizations
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