Replication Data for: Terahertz Spintronic Magnetometer (TSM) (doi:10.21979/N9/WJDQAH)

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Replication Data for: Terahertz Spintronic Magnetometer (TSM)

doi:10.21979/N9/WJDQAH

DR-NTU (Data)

2022-05-13

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Agarwal Piyush; Yang Yingshu; Lourembam James; Medwal Rohit; Battiato Marco; Singh Ranjan, 2022, "Replication Data for: Terahertz Spintronic Magnetometer (TSM)", https://doi.org/10.21979/N9/WJDQAH, DR-NTU (Data), V1

Replication Data for: Terahertz Spintronic Magnetometer (TSM)

doi:10.21979/N9/WJDQAH

Agarwal Piyush (Nanyang Technological University)

Yang Yingshu (Nanyang Technological University)

Lourembam James (Agency for Science, Technology and Research)

Medwal Rohit (Nanyang Technological University)

Battiato Marco (Nanyang Technological University)

Singh Ranjan (Nanyang Technological University)

LabVIEW

NRF-CRP23-2019-0005

MOE2019-T2-1-058

A18A6b0057

NAP-SUG

DR-NTU (Data)

Singh Ranjan

Agarwal Piyush

2022-05-13

https://doi.org/10.21979/N9/WJDQAH

Physics, Physics, spintronic terahertz emission, terahertz hysteresis, terahertz charge current, terahertz magnetometer, THz-H hysteresis

A ferromagnetic metal consists of localized electrons and conduction electrons coupled through strong exchange interaction. Together, these localized electrons contribute to the magnetization of the system, while conduction electrons lead to the formation of spin and charge current. Femtosecond out of equilibrium photoexcitation of ferromagnetic thin films generates a transient spin current at ultrafast timescales that have opened a route to probe magnetism offered by the conduction electrons. In the presence of a neighboring heavy metal layer, the non-equilibrium spin current is converted into a pulsed charge current and gives rise to terahertz emission. Here, we propose and demonstrate a tool known as the terahertz spintronic magnetometry (TSM). The hysteresis loop obtained by sweeping terahertz (THz) pulse amplitude as a function of the magnetic field is in excellent agreement with the vibrating-sample magnetometer measurements. Further, a modified transfer-matrix method employed to model the THz propagation within the heterostructure theoretically elucidate a linear relationship between the THz pulse amplitude and sample magnetization. The strong correlation thus reveals spintronic terahertz emission as an ultrafast magnetometry tool with reliable in-plane magnetization detection, highlighting its technological importance in the characterization of ferromagnetic thin-films through terahertz spintronic emission spectroscopy.

Experimental data

10.1063/5.0079989

Agarwal, P., Yang, Y., Lourembam, J., Medwal, R., Battiato, M., & Singh, R. (2022). Terahertz spintronic magnetometer (TSM). Applied Physics Letters, 120(16), 161104.

10356/157912

Agarwal, P., Yang, Y., Lourembam, J., Medwal, R., Battiato, M., & Singh, R. (2022). Terahertz spintronic magnetometer (TSM). Applied Physics Letters, 120(16), 161104.

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afm data.jpg

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Figure S3: (a) AFM image of bilayer Qz/CoFeB(1.8nm)/Pt(2nm) (b) AFM image of trilayer Qz/W(2nm)/CoFeB(1.8nm)/Pt(2nm) (c) AFM image of monolayer Qz/CoFeB(5nm). A very low mean roughness indicates the uniform surface for all the samples. Moreover, considering the translation of a small fraction of roughness from the 0.5mm thick substrate, the measured roughness is an overestimated value of actual roughness from the thin films. The mean and RMS roughness is calculated for the white square of dimension 5μm x 5μm.

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CoFeB0002.ibw

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Figure S3(c): AFM file for Qz/CoFeB

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CoFeB_2.txt

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Figure S3(c): AFM roughness calculation for Qz/CoFeB

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CoFeB_Pt0002.ibw

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Figure S3(a): AFM file for Qz/CoFeB/Pt

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CoFeB_Pt_2.txt

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Figure S3(a): AFM roughness calculation for Qz/CoFeB/Pt

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Figure 1~b,c.opj

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Figure 1(b,c): Comparing hysteresis measurement from heterostructure when the magnetic field is applied perpendicular to FM easy axis (b) M-H hysteresis measured from commercial VSM system (c) THz hysteresis measured from TSM

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Figure 1~d,e.opj

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Figure 1(d,e): Comparing hysteresis measurement from heterostructure when the magnetic field is applied parallel to FM easy axis (EA) (d) M-H hysteresis measured from commercial VSM system (e) THz hysteresis measured from TSM system.

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Figure 2~a.opj

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Figure 2(a): THz amplitude and charge current when the applied magnetic field is perpendicular to the FM easy axis: THz-H hysteresis measured at variable laser fluence on Quartz/Co40Fe40B20(1.8nm)/Pt(2nm)

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Figure 2~b.opj

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Figure 2(b): THz amplitude and charge current when the applied magnetic field is perpendicular to the FM easy axis: THz pulse amplitude (black spheres) and coercivity (blue spheres) as a function of laser fluence. Solid lines are drawn to guide the eye

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Figure 2~c.opj

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Figure 2(c): THz amplitude and charge current when the applied magnetic field is perpendicular to the FM easy axis: Theoretically calculated terahertz pulse at different field-dependent magnetization states. THz pulses are shifted in time for easier visualisation.

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Figure 2~d.opj

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Figure 2(d): THz amplitude and charge current when the applied magnetic field is perpendicular to the FM easy axis: Measured THz pulse at different field-dependent magnetization states.

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Figure 2~e.opj

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Figure 2(e): THz amplitude and charge current when the applied magnetic field is perpendicular to the FM easy axis: Theoretically calculated transient charge current manifested in the HM layer, at different field-dependent magnetization states

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Figure 2~f.opj

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Figure 2(f): THz amplitude and charge current when the applied magnetic field is perpendicular to the FM easy axis: Experimentally observed THz amplitude shown using black spheres and theoretically calculated THz amplitude shown using solid blue line demonstrate linear relation between the THz pulse amplitude and charge current amplitude

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Figure 3~b.opj

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Figure 3(b): THz-H hysteresis in Quartz/W(2nm)/Co40Fe40B20(1.8nm)/Pt(2nm) : M-H hysteresis measured using the commercial VSM

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Figure 3~c.opj

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Figure 3(c): THz-H hysteresis in Quartz/W(2nm)/Co40Fe40B20(1.8nm)/Pt(2nm) : THz-H hysteresis measured using the TSM.

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Figure 3~d.opj

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Figure 3(d): THz-H hysteresis in Quartz/W(2nm)/Co40Fe40B20(1.8nm)/Pt(2nm) : Theoretically calculated individual and total charge current in the HM layer. Results depict a constructive phase match between jc(Pt) (solid red line) and jc(W) (solid blue line) yielding jc(total) (solid green line).

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Figure 3~e.opj

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Figure 3(e): THz-H hysteresis in Quartz/W(2nm)/Co40Fe40B20(1.8nm)/Pt(2nm) : Theoretically calculated THz pulse amplitude as a function of total charge current amplitude. E(Pt) (solid red line), E(W) (solid blue line) constructively interfere to yield a total E(total) (solid green line).

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Figure 4~b.opj

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Figure 4(b): THz-H hysteresis in Quartz/Co40Fe40B20(5nm): Terahertz pulse recorded from Qz/CoFeB upon illuminating femtosecond laser from both standard (solid black line) and flipped side (solid blue line) of the heterostructure. An apparent phase reversal of terahertz emission denotes spin transport as an underlying principle behind the emission. Inset shows the 87% terahertz transmission observed from the quartz substrate. To compensate for an additional terahertz absorption from quartz, specifically in Laser/CoFeB/Qz configuration, a factor of 1/0.87 is multiplied.

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Figure 4~c.opj

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Figure 4(c): THz-H hysteresis in Quartz/Co40Fe40B20(5nm): M-H hysteresis using the commercial VSM system

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Figure 4~d.opj

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Figure 4(d): THz-H hysteresis in Quartz/Co40Fe40B20(5nm): THz-H hysteresis measured using the TSM system. An opposite phase of THz emission was observed in Qz/CoFeB compared to emission from Qz/CoFeB/Pt or Qz/W/CoFeB/Pt. The effect arises due to spin transport in the negative direction from CoFeB towards the interface with the substrate. (Coercivity is denoted in green color).

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Figure S2~a.opj

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Figure S2(a): Relation between THz amplitude and charge current when the applied magnetic field is parallel to the FM easy axis in CoFeB/Pt : Theoretically calculated terahertz pulse at different field-dependent magnetization states. THz pulse shifted in time axis to show clear representation

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Figure S2~b.opj

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Figure S2(b): Relation between THz amplitude and charge current when the applied magnetic field is parallel to the FM easy axis in CoFeB/Pt : Measured THz pulse at different field-dependent magnetization states

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Figure S2~c.opj

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Figure S2(c): Relation between THz amplitude and charge current when the applied magnetic field is parallel to the FM easy axis in CoFeB/Pt : Theoretically calculated transient charge current manifested in the HM layer, at different magnetization states

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Figure S2~d.opj

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Figure S2(d): Relation between THz amplitude and charge current when the applied magnetic field is parallel to the FM easy axis in CoFeB/Pt : Solid black and blue lines demonstrates linear relation between the THz pulse amplitude and charge current amplitude. Experimentally observed THz amplitude shown using black spheres and theoretically calculated THz amplitude shown using blue spheres.

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Figure S5.opj

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Figure S5: Relation between THz emission from Qz/W/CoFeB/Pt, Qz/CoFeB/Pt, and Qz/CoFeB, for 0.15mJ/cm2 at saturation magnetic field of 100 Oe.

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W_CoFeB_Pt0001.ibw

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Figure S3(b): AFM file for Qz/W/CoFeB/Pt

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W_CoFeB_Pt_1.txt

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Figure S3(b): AFM roughness calculation for Qz/W/CoFeB/Pt

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