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.

(1.3) VCMA: Measurement of dependence of Hall angle, Anomalous Hall effect (AHE), Inverse Spin Hall effect on gate voltage

(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 .

(2.3) VCMA: ""Field- like torque" ""Damp- like torque". Measurement of dependence of PMA on gate voltage.

(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.

(3.3) VCMA: dependence of magnetization switching parameters on gate voltage.

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Details of Measurement Methods are here

 

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Volt 40A (Ta(2 nm)/ FeB(1.3 nm)/ MgO(5.1 nm)/ Ta(1nm)/ Ru(5 nm))

 

fabrication: Ret14 (stepper only, no EB)

Raw data Volt40.zip (.dat files and origin 9 files)

(7zip (free) download is here)

Conductivity: 0.023-0.029 S/m²

Anisotropy field H_anis =4.2 kGauss

Coercive field = 170 Oe-220 Oe;

Hall angle measured=290- 390 mdeg

Intrinsic Hall angle of FeB= 736- 990 mdeg;

Gap region etched: FeB is fully etched, stopped at FeB/ Ta interface

 

size: all samples:

nanowire width: 3 μm; nanomagnet length: 3 μm

 

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magnetization- switching parameters:

retention time τ_ret

(gate): L55-> 10²¹ s; R71-> 10^21.5 s; R43-> 10⁶ s;

(gap): L55-> 10⁹ s; R71-> 10¹⁶ s;

size of nucleation domain:

(gate): L55-> 40 nm; R71-> 44 nm; R43-> 43 nm

(gap): L55-> 25 nm; R71-> 50 nm

coercive field H_c:

(gate): L55-> 370 Oe; R71->310 Oe R43-> 100 Oe

(gap): L55-> 310 Oe; R71-> 280 Oe

parameter Δ :

(gate): L55-> 120; R71->100 R43-> 120

(gap): L55-> 60; R71-> 135

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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=2.5385

 

(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 Volt40: Ta(2 nm)/ FeB(1.3 nm)/ MgO(5.1 nm)/ Ta(1nm)/ 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:( L55 gate) α_ISHE,0.5= 211 mdeg; α_AHE,0.5= 475 mdeg; α_OHE=0.2 mdeg/kG; H_p=20.3 kG;

sample:( R21 gate) α_ISHE,0.5= 222 mdeg; α_AHE,0.5= 753 mdeg; α_OHE=0.2 mdeg/kG; H_p=13.6 kG;

sample:( R43 gate) α_ISHE,0.5= 254 mdeg; α_AHE,0.5= 850 mdeg; α_OHE=0.2 mdeg/kG; H_p=12.4 kG;

sample:( R71 gate) α_ISHE,0.5= 525mdeg; α_AHE,0.5= 327 mdeg; α_OHE=0.2 mdeg/kG; H_p=21.6 kG;

sample:( R71 gate) α_ISHE,0.5= 504mdeg; α_AHE,0.5= 231 mdeg; α_OHE=0.2 mdeg/kG; H_p=21.0 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) fig.4b.Current- dependence of ISHE (∂αHall/∂Hz i)     fig.4c.Dependence of AHE on polarity of current j fig.4d.Dependence of ISHE on polarity of current j ΔAHE= (αHall(j)-αHall(-j))/2/αHall(j) ΔISHE= (ISHE(j)-ISHE(-j))/2 fig.4e. Hall angle αHall at different current j fig.4f.∂αHall/∂Hz at different different current j sample: R21B gate. Dependence of AHE (αHall) is substantial and obvious sample R21B gate. Dependence of ISHE is weak.

details of this measurement method is here

Sample Volt40: Ta(2 nm)/ FeB(1.3 nm)/ MgO(5.1 nm)/ Ta(1nm)/ Ru(5 nm)

click on image to enlarge it

 

Features

(temperature)

dependence on current magnitude

(AHE vs I² ): strong 3% decrease at current of 50 mA/ μm²

(ISHE vs I² ): weak 0.2 mdeg/kG decrease at 50 mA/ μm²

(Spin- orbit torque)

dependence on current polarity

(AHE(I)-AHE(-I)):moderate ~0.5 % (L55 gate: large 0.8 %); slope: all negative; saturation: at low current of 25 mA/ μm²; max change ~0.5 % (L55 gate: 0.8 %).

(ISHE(I)-ISHE(-I)): very small (~0.1 mdeg/kG)

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AHE & ISHE vs gate voltage. VCMA effect

Measurement 1. Dependence of Anomalous Hall effect (AHE) & Inverse Spin Hall effect (ISHE) on gate voltage. Effect of Voltage-Controlled Magnetic Anisotropy (VCMA)

 

 

VCMA. Hall angle, Anomalous Hall effect (AHE), Inverse Spin Hall effect vs gate voltage

fig.5a. dependence of AHE (Hall angle αHall) on gate voltage fig.5b.dependence of ISHE (∂αHall/∂Hz) on gate voltage normalized change of AHE vs gate voltage. nor AHE=(AHE(V)-AHE(V=1))/AHE(V).   fig.5c. Hall angle αHall at different different gate voltages fig.5d.∂αHall/∂Hz at different different gate voltages Sample. Only at Vgate=+0.7 V there is a difference Sample R71. Dependence on Vgate is weak.

details of this measurement method is here

Sample Volt40: Ta(2 nm)/ FeB(1.3 nm)/ MgO(5.1 nm)/ Ta(1nm)/ Ru(5 nm)

click on image to enlarge it

Features

 

dependence on gate voltage

(AHE vs V_gate ): moderate 1.5 % ; slope: unclear

(ISHE vs V_gate ): moderate 0.7 mdeg/kG; slope: negative; saturation: = V_gate=+1 V

 

 

 

 

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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 4.5 kG Offset magnetic field Hoff measured when in-plane magnetic field is scanned along metallic wire. 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 Volt40: 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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Spin-orbit torque vs PMA

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 Volt40: Ta(2 nm)/ FeB(1.3 nm)/ MgO(5.1 nm)/ Ta(1nm)/ Ru(5 nm)

click on image to enlarge it

 

Spin-orbit torque (SOT). 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 decreases proportionally 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 R73

details of this measurement method is here

click on image to enlarge it

 

 

 

 

 

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VCMA vs PMA

 

VCMA. Measurement of dependence of PMA on gate voltage

dependence of anisotropy field on gate voltage ∂Hanis/∂V. Scan is along wire. dependence of anisotropy field on gate voltage ∂Hanis/∂V. Scan is perpendicularly to wire.     dependence of offset field on gate voltage ∂Hoff/∂V. Scan is along wire. dependence of offset field on gate voltage ∂Hoff/∂V. Scan is perpendicularly to wire.

details of this measurement method is here

Sample Volt40: Ta(2 nm)/ FeB(1.3 nm)/ MgO(5.1 nm)/ Ta(1nm)/ Ru(5 nm)

click on image to enlarge it

 

 

 

Voltage-controlled magnetic anisotropy (VCMA). Measurement of dependence of anisotropy field Hanis and offset magnetic field Hoff on gate Voltage

Dependence of anisotropy field Hanis on gate voltage V "Field- like torque". Dependence of offset magnetic field Hoff on gate voltage V. Scan is along wire. "Damp- like torque". Dependence of offset magnetic field Hoff on gate voltage V. Scan is perpendicularly to wire. Hanis is linearly proportional to the gate voltage. Slope is negative. There is a weak saturation at negative voltage. Measurement is under perpendicular magnetic field H is + 0.8 kG. Dependence is weak. Measurement is under perpendicular magnetic field H is + 0.8 kG. Dependence is weak.. Measurement is under perpendicular magnetic field H is + 0.8 kG. Dependence of anisotropy field Hanis on perpendicularly applied magnetic field H 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. . .

Data of Sample R43

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 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(j)-HC(j=0))/HC(j). 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 R71 gate Switching from spin-up to spin-down state. The right- side of hysteresis loop. Sample R71 gate 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 R71 gate

details of this measurement method is here

Sample Volt40: Ta(2 nm)/ FeB(1.3 nm)/ MgO(5.1 nm)/ Ta(1nm)/ Ru(5 nm)

click on image to enlarge it

 

 

VCMA vs Coercive field

 

 

VCMA. Measurement of dependence of PMA on gate voltage.

dependence of normalized coercive field HC on gate voltage dependence of domain size on gate voltage Raw Data. Switching time vs applied magnetic field H at different gate voltage HC is normalized as HC(%)= (HC(V)-HC(V=-1V))/HC(V)   Sample: R71 right side

details of this measurement method is here

Sample Volt40: Ta(2 nm)/ FeB(1.3 nm)/ MgO(5.1 nm)/ Ta(1nm)/ Ru(5 nm)

click on image to enlarge it

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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I am strongly against a fake and "highlight" research