Dr. Vadym Zayets

Abstract:

High- precision, high- reproducibility, high- repeatability measurement of magnetic and magneto- transport properties of ferromagnetic nanomagnets using the Hall effect

High-precision measurement of effect of spin-orbit torque (SOT effect): Dependence of magnetic and magneto- transport properties on electrical current

High-precision measurement of effect of voltage-controlled magnetic anisotropy (VCMA effect): Dependence of magnetic and magneto- transport properties on a gate voltage

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Measurements

(measurement 1) Measurement of Hall angle vs external perpendicular magnetic field

(1.1) Measurements of Hall angle, Anomalous Hall effect (AHE), Inverse Spin Hall effect (Sample dependence)

(1.2) Spin-orbit torque: Measurement of dependence of Hall angle, Anomalous Hall effect (AHE), Inverse Spin Hall effect on current magnitude and polarity.

(measurement 2) Measurement of anisotropy field vs external perpendicular magnetic field

(2.1) Measurement of PMA & Anisotropy field

(2.2) Spin-orbit torque: ""Field- like torque" ""Damp- like torque". Measurement of dependence of PMA on the electrical current .

(measurement 3) Measurement of magnetization switching under external perpendicular magnetic field

(3.1) Measurement of coercive field H_C, retention time, size of nucleation domain, parameter delta Δ

(3.2) Spin-orbit torque: Current dependence of magnetization switching parameters.

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Details of Measurement Methods are here

 

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Volt 50B (Ta(3)/ FeB(1.1)/ MgO(7)/ W(1)/ Ru(5))

 

 

Raw data Volt50.zip (.dat files and origin 9 files)

(7zip (free) download is here)

Conductivity: 0.039-0.62 S/m²

Anisotropy field H_anis =5kGauss

Coercive field = 170 Oe-220 Oe;

Hall angle measured=450- 800 mdeg

Intrinsic Hall angle of FeB= 1677- 2982 mdeg;

Gap region etched: stopped at MgO/ FeB interface

 

 

 

 

 

 

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magnetization- switching parameters:

retention time τ_ret

(gate): free35-> 10¹⁶ s; free36-> 10⁶ s; free56-> 10⁶ s; free82-> 10¹⁶ s;

(gap): free35-> 10⁷ s; free36-> 10¹⁴ s; free56-> 10⁸ s; free82-> 10¹⁰ s;

size of nucleation domain:

(gate): free35-> 55 nm; free36-> 35 nm; free56-> 30 nm; free82-> 55 nm;

(gap): free35-> 38 nm; free36-> 50 nm; free56-> 35 nm; free82-> 40 nm;

coercive field H_c:

(gate): free35-> 180 Oe; free36-> 205 Oe; free56-> 220 Oe; free82-> 175 Oe;

(gap): free35-> 180 Oe; free36-> 220 Oe; free56-> 200 Oe; free82-> 145 Oe;

parameter Δ :

(gate): free35-> 240; free36-> 100; free56-> 60; free82->240;

(gap): free35-> 110; free36-> 190; free56-> 150; free82->170;

 

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sizes of nanomagnets & conductivity σ

fabricated 180320

(free 36): wire width: 200 nm; nanomagnet length: 100 nm; σ = 0.0446 S/m²

(free 35): wire width: 100 nm; nanomagnet length: 100 nm; σ = 0.039 S/m²

(free 56): wire width: 200 nm; nanomagnet length: 100 nm; σ = 0.049 S/m²

(free 82): wire width: 200 nm; nanomagnet length: 200 nm; σ = 0.063 S/m²

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Since the nanowire is double- layer, which consists of Ta and FeB layer, the Hall angle α_{Hall, FeB} in FeB can be calculated from measured Hall angle α_{Hall, measured} (See here) as

where

t_FeB, t_Ta, σ_FeB,σ_Ta are thicknesses and conductivities of FeB and Ta metals.

 

k_double=3.7273

 

 

 

 

 

 

 

 

 

(measurement 1) Measurement of Hall angle vs external perpendicular magnetic field Hz

 

 

 

Hall angle, Anomalous Hall effect (AHE), Inverse Spin Hall effect (Sample dependence)

Hall angle αHall 1st derivation ∂αHall/∂Hz 2nd derivation ∂2αHall/∂Hz2 αHall and therefore strength of AHE is substantially different for each nanomagnet ∂αHall/∂Hz is different for ~10 % for each sample with correspondent difference of ∂2αHall/∂Hz2, which means that the strength of ISHE is different for each nanomagnet

details of this measurement method is here

Sample Volt50: Ta(3 nm)/ FeB(1.1 nm)/ MgO(7 nm)/ W(1 nm) /Ru(5 nm)

click on image to enlarge it

Fitting of Hall angle

The Hall angle α_Hall , its 1st derivation ∂α_Hall/∂H_z and its 2d derivation ∂²α_Hall/∂H_z² is simultaneously fitted by equation (See here)

where α_OHE is Hall angle of Ordinary Hall effect, α_AHE is Hall angle of Anomalous Hall effect and where α_ISHE is Hall angle of Inverse Spin Hall effect

There is an ambiguity for α_ISHE and α_AHE, which depends on unknown spin polarization sp

where sp is the spin polarization of conduction electrons, α_AHE,0.5 is α_AHE at sp=0.5, α_ISHE,0.5 is α_ISHE at sp=0.5

result of fitting:

sample:( free35 gate) α_ISHE,0.5= 187 mdeg; α_AHE,0.5= 1513 mdeg; α_OHE=0.2 mdeg/kG; H_p=8.41 kG;

sample:( free36 gate) α_ISHE,0.5= 213 mdeg; α_AHE,0.5= 1777 mdeg; α_OHE=0.2 mdeg/kG; H_p=9.72 kG;

sample:( free56 gate) α_ISHE,0.5= 207 mdeg; α_AHE,0.5= 1980mdeg; α_OHE=0.2 mdeg/kG; H_p=9.5 kG;

sample:( free82 gate) α_ISHE,0.5= 284 mdeg; α_AHE,0.5= 2701 mdeg; α_OHE=0.2 mdeg/kG; H_p=10.83 kG;

 

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AHE & ISHE vs current & current polarity. SOT effect

Measurement 1. Dependence of Anomalous Hall effect (AHE) & Inverse Spin Hall effect (ISHE) on current and current polarity. Effect of Spin-Orbit Torque (SOT)

 

Spin-orbit torque. Hall angle, Anomalous Hall effect (AHE), Inverse Spin Hall effect vs current

fig.4a. Current- dependence of AHE (Hall angle αHall) Current- dependence of ISHE (∂αHall/∂Hz i)     Dependence of AHE on polarity of current j Dependence of ISHE on polarity of current j ΔAHE= (αHall(j)-αHall(-j))/2 ΔISHE= (ISHE(j)-ISHE(-j))/2 Hall angle αHall for different current j   sample free 82. Dependence of AHE (αHall) is substantial and obvious sample free 82. Dependence of ISHE is weak.

details of this measurement method is here

Sample Volt50: Ta(3 nm)/ FeB(1.1 nm)/ MgO(7 nm)/ W(1 nm) /Ru(5 nm)

click on image to enlarge it

Features

(temperature)

dependence on current magnitude

(AHE vs I² ): strong 2.5-4 % decrease at current of 100 mA/ μm²; 1-2.5 % decrease at current of 50 mA/ μm²

(ISHE vs I² ): weak; strange polarity

(Spin- orbit torque)

dependence on current polarity

(AHE(I)-AHE(-I)): moderate ~0.5 % ; slope: all negative; saturation: at 50 mA/ μm²;

(ISHE(I)-ISHE(-I)): very small (0.04 mdeg/kG)

 

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(measurement 2) Measurement of anisotropy field vs external perpendicular magnetic field Hz

details about measurement method is here and here

 

Measurement of PMA. Anisotropy field

Anisotropy field Hanis Offset magnetic field Hoff . Scan is along wire. Offset magnetic field Hoff . Scan is perpendicularly to wire. Anisotropy field Hanis vs external perpendicular magnetic field Hz. Hanis is about 5 kG and variation from sample to sample is about 0.5 kG. Offset magnetic field Hoff measured when in-plane magnetic field is scanned along metallic wire. There is a substantial difference between samples and a substantial difference between positive and negative scans of Hz. At Hz =7 kG, Hoff = between 50-100 G for different samples. The dependence is linear with some periodical modulation. Offset magnetic field Hoff measured when in-plane magnetic field is scanned perpendicularly to metallic wire. There is a substantial difference between samples and a substantial difference between positive and negative scans of Hz. At Hz =7 kG, Hoff = between -10-40G for different samples. The dependence is slightly linear (nearly a constant) with a substantial periodical modulation.

details of this measurement method is here

Sample Volt50: Ta(3 nm)/ FeB(1.1 nm)/ MgO(7 nm)/ W(1 nm) /Ru(5 nm)

click on image to enlarge it

 

 

Spin-orbit torque. Measurement of dependence of PMA on the electrical current j.

"Field- like torque". Current- dependence of offset field ∂Hoff/∂j. Scan is along wire. "Damp- like torque". Current- dependence of offset field ∂Hoff/∂j. Scan is perpendicularly to wire. ∂Hoff/∂j~ 0.1 Gauss/(mA/ μm2).E.g. at j=100 mA/ μm2, change of offset field ΔHoff=10 Gauss. There are clear oscillations. There is a substantial difference between positive and negative scans of Hz. ∂Hoff/∂j~ 0.18 Gauss/(mA/ μm2).E.g. at j=100 mA/ μm2, change of offset field ΔHoff=18 Gauss. There are clear oscillations. There is a substantial difference between positive and negative scans of Hz. Current- dependence of anisotropy field∂Hanis/∂j. Scan is along wire. Current- dependence of anisotropy field∂Hanis/∂j. Scan is perpendicularly to wire. ∂Hanis/∂j~ 0.8 Gauss/(mA/ μm2).E.g. at j=100 mA/ μm2, change of anisotropy field ΔHanis=80 Gauss. There are clear oscillations. Amplitude of oscillations increases at a larger Hz. There is a substantial difference between positive and negative scans of Hz. ∂Hanis/∂j~ 0.8 Gauss/(mA/ μm2).E.g. at j=100 mA/ μm2, change of anisotropy field ΔHanis=80 Gauss. There are clear oscillations. Amplitude of oscillations increases at a larger Hz. There is a substantial difference between positive and negative scans of Hz.

details of this measurement method is here

Sample Volt50: Ta(3 nm)/ FeB(1.1 nm)/ MgO(7 nm)/ W(1 nm) /Ru(5 nm)

click on image to enlarge it

 

Spin-orbit torque. Measurement of dependence of anisotropy field Hanis and offset magnetic field Hoff on the electrical current j.

"Field- like torque". Dependence of offset magnetic field Hoff on current j. Scan is along wire. "Damp- like torque". Dependence of offset magnetic field Hoff on current j. Scan is perpendicularly to wire. Dependence of anisotropy field Hanis on current j. Dependence is linear. Slope is positive. Measurement is under perpendicular magnetic field H is + 0.8 kG. Dependence is linear. Slope is positive. Measurement is under perpendicular magnetic field H is + 0.8 kG. Hanis is proportional to j2 due to heating. Also, Hanis is proportional to polarity of current due to SOT effect (dependence is different for +j and -j current). Measurement is under perpendicular magnetic field H is + 0.8 kG. Dependence of offset magnetic field Hoff on perpendicularly applied magnetic field H. Scan is along wire. Dependence of offset magnetic field Hoff on perpendicularly applied magnetic field H. .Scan is perpendicularly to wire. Dependence of anisotropy field Hanis on perpendicularly applied magnetic field H . .

Data of Sample free36 gate

details of this measurement method is here

click on image to enlarge it

 

 

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(measurement 3) Measurement of magnetization switching under external perpendicular magnetic field Hz

SOT effect. Current dependence of magnetization switching parameters.

Coercive field HC Normalized change of coercive field HC vs current Dependence of HC on polarity of current j. SOT effect A substantial difference of HC from sample to sample (140-220 Oe). HC is reduced due to heating as HC~ j2. Additionally, coercive field linearly proportional to current HC~j due to SOT effect ΔHC= (HC(j)-HC(-j))/2. The change of HC with reverse of polarity of current. retention time Size of nucleation domain Delta Δ       Raw Data. Switching time vs applied magnetic field H and bias current. Raw Data. Switching time vs applied magnetic field H and bias current Dependence of HC on polarity of current j. SOT effect. Switching from spin-down to spin-up state. The left- side of hysteresis loop. Sample free56_gap Switching from spin-up to spin-down state. The right- side of hysteresis loop. Sample free56_gap ΔHC= (HC(j)-HC(-j))/2. The change of HC with reverse of polarity of current. Data of both gate and gap nanomagnet and from left and right- side switching of the hysteresis loop. Sample free56_gap

details of this measurement method is here

Sample Volt50: Ta(3 nm)/ FeB(1.1 nm)/ MgO(7 nm)/ W(1 nm) /Ru(5 nm)

click on image to enlarge it

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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I am strongly against a fake and "highlight" research