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Tunneling Magnetoresistance(TMR)

Gokaran Shukla

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Layout

Introduction

Physical Models

Role ofinsulating oxide in TMR

Analysis of ZnO GaN, AlN as Tunnel Barrier

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Row 1 Row 2 Row 3 Row 4

0

2

4

6

8

10

12

Column 1

Column 2

Column 3

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Jullier Model

Model :

Short coming: Independence from geometry andthe electronic structure of barrier layer

Sign of P

M. Julliere, Phys. Lett. 54A, 225 (1975)

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Slonczewski's Model

Butleret.alPRB 56, 11827 (1997)

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Butler Model

Model count Geometery and electronics structureof both Ferromagnet & insulating barrier

Its also count curvature effect of wave function

Butleret.alPRB 56, 11827 (1997)

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Wave function Symmetry

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Example

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Example

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Role ofInsulating Oxide

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Role ofInsulating Oxide

JOURNAL OF APPLIED PHYSICS 102, 083710 2007

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Role ofInsulating Oxide

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Characteristic features about InsulatorOxide

Insulator barrier height

Insulator barrier width(thickness)

Crystalinity of the barrier material

Electronic structure of the barrier

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Physics behind TMR

Orientation of both Ferromagnetic Electrode

Insulator barrier height, barrier thickness,crystalinity and elctronic structure of electrode as

well as barrier material.

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Why ZnO GaN AlN ?

ZnO is a ferroelectric material, and this material is thebackbone of Display industries.

Although ZnO has a smaller band gap than MgO/Al2O3 butthe presensce of spontaneous polarization could assist in spin

filtering and thus direct spin injection could be possible in ZnO Blue LED and Blue Laser based on the GaN/AlN . So, spin

polarized light could possible by direct spin injection in thesematerial.

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Analysis of ZnO as Tunnel Barrier

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Complex Band

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Co & Fe Band

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GaN as a Tunnel Barrier

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AlN Transport

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AlN complex band

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Co|ZnO|Co Structure Stability Analysis

Structure TotalEnergy(eV) Max Force(eV/A)

Pressure(KBar)

7 Layer of ZnO

Co_Vacant -93396.344897 0.048247 62.99910693

Co_Oxygen -93393.126235 0.029384 97.49865198

Co_Zinc -93393.126115 0.029484 97.40007053

3 Layer of ZnO

Co_Vacant

Co_Oxygen -61162.603546 0.035568 99.44513085

Co_Zinc

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Conclusion

Discussed about TMR principle.

ZnO GaN AlN as a tunnel barier for spin filtering withmajor goal is to direct spin injection in these materials.

It seems that Co would prefer vacant site rather thanOxygen/Zinc. This is very opposite from Fe|MgO|Fecase where Fe is on top of Oxygen.

A proper electrode material need to be look which

fulfill the desire for GaN and AlN

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Thanks for your kind Attention