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

Coercive field is about 40 Oe and retention time is about a few minutes. The retention time is too short for a precise measurement.

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Details of Measurement Methods are here

 

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Volt54A (Ret14) Ta(2.5 nm)/ FeB(1.1 nm)/ MgO(6 nm)/ Ta(1 nm)/ Ru(5 nm)

 

fabrication: Ret14 (stepper only, no EB)

MgO 220C/360C

Raw data Volt54A.zip (.dat files and origin 9 files)

(7zip (free) download is here)

Conductivity: 0.055-0.06 S/m2

Anisotropy field H_anis =2.5 kGauss

Coercive field = 20 Oe-70 Oe;

Hall angle measured=320- 370 mdeg

Intrinsic Hall angle of FeB= 1047 - 1211 mdeg;

Gap region etched: FeB is partially etched, stopped in middle of FeB

 

size: all samples:

nanowire width: 3 μm; nanomagnet length: 3 μm

 

 

 

 

 

 

 

 

 

 

 

 

 

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magnetization- switching parameters:

retention time τ_ret

(gate): L68-> 10⁵ s; R26-> 10^3.9 s; L34-> 10⁴ s;

size of nucleation domain:

(gate): L68-> 70 nm; R26-> 64 nm; L34-> 70 nm

coercive field H_c:

(gate): L68-> 34 G; R26->32 G R43-> 26 G

parameter Δ :

(gate): L68-> 185; R26->134; L34-> 190

 

 

 

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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=3.2727

 

 

size: all samples:

nanowire width: 3 μm; nanomagnet length: 3 μm

 

 

 

 

 

 

 

 

(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 Volt54A Ta(2.5 nm)/ FeB(1.1 nm)/ MgO(6 nm)/ Ta(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:( L16B) α_ISHE,0.5= 395 mdeg; α_AHE,0.5= 627 mdeg; α_OHE=0.2 mdeg/kG; H_p=5.37 kG;

sample:( L20) α_ISHE,0.5= 424 mdeg; α_AHE,0.5= 717 mdeg; α_OHE=0.2 mdeg/kG; H_p=5.35 kG;

sample:( L70) α_ISHE,0.5= 351 mdeg; α_AHE,0.5= 695 mdeg; α_OHE=0.2 mdeg/kG; H_p=5.84 kG;

sample:( R26) α_ISHE,0.5= 549 mdeg; α_AHE,0.5= 672 mdeg; α_OHE=0.2 mdeg/kG; H_p=6.14 kG;

sample:( R66) α_ISHE,0.5= 405 mdeg; α_AHE,0.5= 698 mdeg; α_OHE=0.2 mdeg/kG; H_p=5.33 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 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: L20B. Dependence of AHE (αHall) is substantial and obvious sample L20B gate. Dependence of ISHE is weak.

details of this measurement method is here

Sample Volt54A Ta(2.5 nm)/ FeB(1.1 nm)/ MgO(6 nm)/ Ta(1 nm)/ Ru(5 nm)

click on image to enlarge it

Features

(temperature)

dependence on current magnitude

(AHE vs I² ): strong 4% decrease at current of 50 mA/ μm²; (fig.4a)

(ISHE vs I² ):weak, 0.2 mdeg/kG decrease at 50 mA/ μm² (fig.4b)

(Spin- orbit torque)

dependence on current polarity

(AHE(I)-AHE(-I)):weak (most of samples); moderate 0.6 % (samples: R41,R42) slope: negative e; saturation: at 40 mA/ μm²; (fig.4c)

(ISHE(I)-ISHE(-I)): very small (~0.1 mdeg/kG) (fig.4d)

 

 

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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. normalized 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. Dependence on Vgate is weak, but clear Sample ud66. Dependence on Vgate is weak, but distinguishable.

details of this measurement method is here

Sample Volt54A Ta(2.5 nm)/ FeB(1.1 nm)/ MgO(6 nm)/ Ta(1 nm)/ Ru(5 nm)

click on image to enlarge it

Features

 

dependence on gate voltage

(AHE vs V_gate ): moderate 0.8 % ; slope: negative; saturation: none

(ISHE vs V_gate ): moderate 0.3 mdeg/kG; slope: positive; saturation: none

 

 

 

 

 

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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. Up to =2.5 kG, there is a peak and diversion from a strait line. There is a weak difference between positive and negative scans of Hz. 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 VolA54: 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 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 Volt54A Ta(2.5 nm)/ FeB(1.1 nm)/ MgO(6 nm)/ Ta(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 L16B

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 Volt54A Ta(2.5 nm)/ FeB(1.1 nm)/ MgO(6 nm)/ Ta(1 nm)/ 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. The dependence of Hanis on gate voltage is substantial. 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 R42C

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

 

Coercive field is about 40 Oe and retention time is about a few minutes. The retention time is too short for a precise measurement.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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I am strongly against a fake and "highlight" research