Dr. Vadym Zayets

Abstract: The effect of spin- dependent conductivity describes the fact that the conductivity of a ferromagnetic metal depend on mutual direction between spins of its localized d- electrons and the spins of its spin- polarized conduction electrons. The GMR effect describes the effect that the conductivity

 

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Content

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Spin- dependent conductivity.

Another Kondo-type magneto- transport effect is the Spin- dependent conductivity. This effect describes the Spin detection effect (See here) and the in-plane giant magnetic resistance (GMR) effect.

This Kondo-type magneto- transport effect is proportional to the scalar product of total spins of localized and conduction electrons:

Since this magnetic current is always along the main current j_M || j_V. the effect can be describe as a change of the total current

as in this case

or conductivity

if φ is the angle between the spin of localized electrons (magnetization) and the spin of conduction electrons and P_s is the spin polarization of the conduction electrons. The spin- dependent conductivity can be described as

 

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Facts about spin dependent conductivity

 

 

(fact 1 about spin- dependent conductivity) Spin-detection

The spin detection effect describes the creation of charge and voltage along diffusion path of a spin current. The origin of the spin- detection effect is the spin- dependent conductivity.

A spin diffusion current is a current of spin without a current of charge. It consists of two currents of spin-polarized and spin-unpolarized electrons, which flow in opposite directions. When

(fact 2 about spin- dependent conductivity) The effect of the spin- dependent conductivity does not contribute to the AMR or the Planar Hall effect

The spin

(fact 3about spin- dependent conductivity) In-plane GMR

The spin

(fact 4 about spin- dependent conductivity) spin- dependent conductivity is large at an interface

The spin

(fact 5 about spin- dependent conductivity) spin- dependent conductivity is large in a material with a low conductivity

The spin

 

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Origins of spin- dependent conductivity

 

 

 

 

 

 

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In-plane Giant Magneto- resistance (GMR) effect

The in-plane GMR effect describes the fact that resistance of a metallic wire, which consists of two ferromagnetic layers separated by a non-magnetic layer, depends on mutual magnetization directions of two ferromagnetic layers. It is the smallest, when magnetization directions are parallel and it is the largest, when the magnetization directions is opposite.

For experimental discovery of the in-plane GMR effect, Prof. Fert and Prof. Grünberg were awarded the Nobel Price in Physics in 2007.

 

(origin 1 of in-plane GMR effect) Spin proximity effect

The spin proximity effect (See details here) describes the fact that the spin polarized conduction electrons diffuses from the first ferromagnetic layer to the second ferromagnetic layer, change the spin polarization in the second layer and as a results the resistivity of the second ferromagnetic layer increases due to the effect of the spin- dependent conductivity.

(origin 2 of in-plane GMR effect) spin- dependent conductivity.

The conductivity of a ferromagnetic metal depends on mutual directions of spins of localized electrons and spins of conduction electrons. When spin-polarized conduction electrons diffuses from one ferromagnetic metal to the second ferromagnetic layer of a different magnetization directions, they make different the in the spin directions of localized and conduction electrons in the second layer and as a result the resistivity of the second layer becomes larger.

 

 

(Origin of in-plane GMR effect):

When the magnetization directions in ferromagnetic layers are parallel, the spin directions of the spin-polarized conduction electrons are also the same and parallel to the magnetization (the spins of localized electrons). In this cases, the resistance of each layer is smallest. When the magnetization directions are opposite, the spin directions of conduction electrons are also opposite. In the case when in the first ferromagnetic layer the number of the spin polarized electrons is substantially larger than in the second ferromagnetic layer, a significant amount of the spin -polarized electrons from first layer diffuses into the second ferromagnetic layer and the spin direction in there become the same as in the first layer and opposite to the magnetization of localized electrons. As a result, the resistivity of the second layer becomes larger. The resistivity of a material is largest when the spin direction conduction electrons is opposite to the spin direction of the localized electrons due to the effect of the spin- dependent conductivity.

 

(note)When the total thickness of wire becomes smaller than the electron mean-free path, the electron gas becomes common through both ferromagnetic layers and the spin polarization is always the same in both layers. When magnetizations directions are parallel, the common spin polarization is the largest and parallel to each magnetization and therefore the resistance of each layer is smallest. When magnetizations directions are opposite, the common spin polarization is small (close to zero).As a result, the resistance becomes larger in each layer.

 

 

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Perpendicular-to-plane Giant Magneto- resistance (GMR) effect

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Questions && Answers

 

 

Why the GMR is called giant? Is it really very gigantic?

No. Actually it is rather small. For example, it rarely exceeds 1% and often even smaller than 0.1 %. In contrast, the tunnel magneto-resistance is often >100 % (at least 100%)

Why then is it called giant?

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I am strongly against a fake and "highlight" research