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more Chapters on this topic:

Introduction

Transport Eqs.

Spin Proximity/ Spin Injection

Spin Detection

Boltzmann Eqs.

Band current

Scattering current

Mean-free path

Current near Interface

Ordinary Hall effect

Anomalous Hall effect, AMR effect

Spin-Orbit interaction

Spin Hall effect

Non-local Spin Detection

Landau -Lifshitz equation

Exchange interaction

sp-d exchange interaction

Coercive field

Perpendicular magnetic anisotropy (PMA)

Voltage- controlled magnetism (VCMA effect)

All-metal transistor

Spin-orbit torque (SO torque)

What is a hole?

spin polarization

Charge accumulation

MgO-based MTJ

Magneto-optics

Spin vs Orbital moment

What is the Spin?

model comparison

Questions & Answers

EB nanotechnology

Reticle 11

 

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Parametric mechanism of Magnetization Reversal.

Part 2. Parametric parameter: Current- induced magnetic field.

Spin and Charge Transport

Abstract:

When a electron current flows through a ferromagnetic nanomagnet, spin- polarized electrons are accumulated at nanomagnet boundaries due to the Spin Hall effect. The magnetic field, which is induced by the spin accumulation, tilts the nanomagnet magnetization from its equilibrium direction. The magnetic field is small, but measurable. At a current density of 65 mA/μm2 the spin- accumulation- induced magnetic field is measured to be about 60 Gauss. Such a small magnetic field tilts the magnetization very slightly. The tilting angle is only about 100 mdeg. However, in case when the electron current and as consequence the spin accumulation and the induced magnetic field are modulated t a frequency close the resonance frequency ωL of the magnetization precession (Larmor frequency), even a small spin-polarization- induced magnetic field is able to enhance resonantly the magnetization precession, which leads to the magnetization reversal.

Furthermore, in the case when this effect occurs in n a magneto- resistive structure the magnetization can be effectively reversed even by a DC current due to a parametric resonance. A random thermal oscillation of magnetization modulates the electrical current due to the magneto-resistance. Both the electron current and the spin- accumulation- induced magnetic field ares modulated precisely at the Larmor frequency. As a result, , the magnetization precession is parametrically enhanced, which causes even larger current modulation. Due to this positive feedback loop, the magnetization precession angle becomes larger and larger until the magnetization reversal. A low threshold current for the magnetization reversal is the major merit of this DC-current- induced magnetization reversal.

page creation date: start April 2021-

Content

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6. Explanation video

 

 

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details about this mechanism of the parametric magnetization reversal can be found here V. Zayets arXiv:2104.13008 (2021), V.Zayets IEEE Transactions on Magnetics (2021)V.Zayets. arXiv:2111.05438 (2021)

(Part 1 is here): General principles of Parametric mechanism of Magnetization Reversal.
(Part 2 is here): Parameter of parametric resonance: Current- induced magnetic field.
(Part 3 is here): Parameter of parametric resonance: Anisotropy field.
(Part 4 is here): Parameter of parametric resonance: Amount of spin injection.

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Current-induced magnetic field H(CI) or HSOT

 

(key property for parametric magnetization reversal) Current-induced magnetic field H(CI) modulates magnetization direction

 

 

origin of current- induced magnetic field H(CI) ( HSOT): spin accumulation at interface

(important): spin direction of accumulated conduction electrons is perpendicular to the spin direction of nanomagnet magnetization
An electric current, which flow through the nanomagnet, creates spin accumulation of spin-polarized conduction electrons (green balls) due to the Spin Hall effect (See here). the magnetic field due to the current- induced spin accumulation is perpendicular to the spin of localized electrons (blue ball). As a result, the spin of localized electrons (magnetization) is tilted towards the in-plane direction.
H(CI) is often called the magnetic field HSOT of the spin- orbit torque (See here)
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(RF modulated current: parametric resonance)When frequency and phase of the electrical current in the resonance with the magnetization precession, the modulation of H(CI) leads to enhancement of magnetization oscillations and further to the magnetization reversal (See details below)

(DC electrical current: positive feedback loop) Under a DC current a thermally- initiated magnetization oscillation is enhanced to a substantial magnetization precession and further to the magnetization reversal due to positive feedback loop. The positive feedback loop is: (1) a small magnetization precession---> (2) modulation of the magneto- resistance ---> (3) modulation of electrical current ---> (4) modulation of the current-induced magnetic field H(CI) ---> (5) parametric enhancement of magnetization precession ---> (6) magnetization precession at a larger precession angle ---> (2) --->(3) ---> (4) ---> (5) --->(6) --> (2)

 

(origin of current-induced magnetic field H(CI): The spin- polarized conduction electrons are accumulated at boundary of the nanomagnet under an electrical current due to the Spin Hall effect . The spin accumulation creates a magnetic field, which is called the H(CI)

(note) As 2021/05 this possible origin of H(CI is only a suggestion

(uniqueness of H(CI)) : the magnetic field, which induced by an electrical current flowing through a nanomagnet, affects the magnetization of nanomagnet itself.

 

Measurement of H(CI)

 

(low- precision measurement) the second- harmonic Hall effect (see here)

(high- precision measurement) method of in-plane- magnetic- filed scan (see here)

 

measured features of H(CI)

(feature 1 of H(CI)) : substantial dependency of the direction and magnitude of on the applied external magnetic field Hz

(feature 2 of H(CI)) : a change of H(CI) due to current change is perpendicular to a change due to Hz change.

 

 

Measurement of SO in-plane magnetic field H||. Dependence on current density

Fig. 2a. Experimental setup

Fig 2b. Component along x-axis

Fig.2c Component along y-axis
The light- blue arrow shows the in-plane SO magnetic field H|| created by the external magnetic field Hz. The red arrow shows H||,j created by the electrical current. Both fields H|| and H||,j are nearly perpendicular to each other. The x-component of H|| reverses its polarity when Hz is reversed. The magnitude of H|| is nearly constant with a weak oscillations. The x-component of H|| decays when Hz increases.
     

Fig.2d. component along x-axis

Fig.2e component along x-axis

Fig.2f. 2D map of H||

The current dependence of In-plane spin-orbit magnetic field H||
sample Volt 54a nanomagnet R42C. Size 3000 nm x 3000 nm. See more details about sample here.
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Current- induced magnetic field

 
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Resonant magnetization reversal by a magnetic field HSO

 
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Magnetization reversal by a DC current

Magnetization reversal by a DC current

 
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Measurement of Current-induced magnetic field in a nanomagnet

Current induced magnetic field

 

dependency on current  
   
 
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Video

Parametric magnetization reversal.

Spin- orbit torque

Conference presentation. Intermag 2021

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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