Slide1 l.jpg
This presentation is the property of its rightful owner.
Sponsored Links
1 / 71

Magnetic Tunnel Junctions PowerPoint PPT Presentation


  • 154 Views
  • Uploaded on
  • Presentation posted in: General

Magnetic Tunnel Junctions. Transfer Hamiltonian. Tunneling Magnetoresistance. Tunneling: see Phil. Mag. 83 , 1255 (2003). k || resolved (partial) DOS in units of states/atom. eV of bcc(100) Fe plotted in the first 2DBZ. Left column is for the majority spin channel

Download Presentation

Magnetic Tunnel Junctions

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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Slide1 l.jpg

Magnetic Tunnel Junctions


Slide2 l.jpg

Transfer Hamiltonian


Slide3 l.jpg

Tunneling Magnetoresistance


Slide4 l.jpg

Tunneling: see Phil. Mag. 83, 1255 (2003)


Slide8 l.jpg

k|| resolved (partial) DOS in

units of states/atom. eV of

bcc(100) Fe plotted in the

first 2DBZ. Left column is

for the majority spin channel

and right column is for the

minority spin channel.

From top to bottom, DOS

for a bulk Fe layer, a free

surface Fe layer and the

isolated electrode surface

Fe layer.

k|| resolved (partial) DOS in units of states/atom. eV of bcc(100) Fe plotted in the first 2DBZ. Left column is for the majority spin channel and right column is for the minority spin channel. From top to bottom, DOS for a bulk Fe layer, a free surface Fe layer and the isolated electrode surface Fe layer.


Slide11 l.jpg

k|| resolved (partial) DOS in

units of states/atom. eV of

fcc(100) Co plotted in the

first 2DBZ. Left column is

for the majority spin channel

and right column is for the

minority spin channel.

From top to bottom, DOS

for a bulk Co layer, a free

surface Co layer and the

isolated electrode surface

Co layer.


Slide14 l.jpg

Also see for resonant states: O.Wunnicke et al. PRB 65, 064425 (2002).


Slide19 l.jpg

k|| resolved (partial) tunneling

conductance of bcc (100)

Fe/vacuum(10)/Fe tunnel

junction at an energy 0.05eV

below the Fermi level (a) only

for the barrier region, and (b)

for the entire junction.


Slide20 l.jpg

zoomed-in view.


Slide21 l.jpg

k|| resolved (partial) tunneling

conductance of the barrier region of a

Co junction in the first 2DBZ when the

magnetizations of the two electrodes are

aligned in parallel(a) majority spin channel,

(b) minority spin channel, and

(c) antiparallelly aligned. The vacuum

barrier is 6 atomic layers thick.


Slide23 l.jpg

The need to diagonalize basis when more than one state

transforms under same irreducible representation

C. Uiberacker and P.M. Levy, PRB 64, 193404 (2001);erratum

PRB 65, 169904 (2002).


Slide28 l.jpg

Fe/ZnSe/Fe


Slide29 l.jpg

Bias dependence of TMR


Slide32 l.jpg

Bias dependence of TMR-trapezoidal barrier

JMR ratio vs. bias for free electron trapezoidal barrier model tunnel junction with a Fermi sea depth of 16eV for majority and 3eV for

minority spins; square barrier height at zero bias is 1eV measured

from Fermi level


Slide34 l.jpg

Oscillating TMR S.Yuasa et al. Science 297, 234 (2002)


Slide38 l.jpg

Ab-initio calculation of JMR for Co/Vac(6)/Cu(p)Co junction;

K. Wang private communication.


Slide39 l.jpg

Tunneling with semiconducting electrodes

For metallic electrodes it is sufficient to have 2-3ML of the

magnetic electrode for spin dependent tunneling (SDT) ;

therefore it is not the spin polarization of the current that

produces SDT. What happens for semiconducting electrodes?

As there is little screening of electrons in semiconductors I

surmise that the SDT with 2-3ML of magnetic semiconducting

electrodes is very different from 20-30 ML.

Also, there will be hole as well as electron conduction; particularly

for holes spin-orbit coupling plays an important role. The spin-orbit

coupling can be detrimental to the polarization of spin currents.


Slide40 l.jpg

  • One can conceptualize spin dependent tunneling in two steps:

  • Presenting spin polarized electrons at the interface of between

  • the electrode and barrier. This is accounted for by the DOS.

  • The decay of wavefunction inside the barrier. There are

  • evanescent states inside the barrier whose decay is given by

  • an imaginary k vector.


Slide45 l.jpg

So what’s new?

The spin Hall effect: Hirsch (1999), Zhang (2000)*

In general the Hall effect is the current or voltage transverse

to the applied electric field. This usually appears when one

applies a magnetic field perpendicular to the electric field;

however in systems that contain spin-orbit coupling one can

have preferential scattering of spins to the left or right of the

current, so that one can produce a Hall voltage in the absence

of a magnetic field. This principle was first enunciated by Mott

and has the formed the basis of Mott spin scattering detectors.

*


Slide46 l.jpg

Then we were told there’s an intrinsic SHE

It seems not!

But can one detect the ISHE?


Slide59 l.jpg

What do the experimentalists say about the ISHE?


Slide62 l.jpg

Molecular spintronics


Slide66 l.jpg

Published online March 6, 2005 in Nature Materials


Slide71 l.jpg

Conclusion


  • Login