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Spintronic operation in antiferromagnets 1 CSRN @Osaka Univ. @Tohoku Univ. Takahiro Moriyama Institute for Chemical Research, Kyoto University Highlights 1. Spin pumping in FM/AFM 2. Terahertz spin pumping in AFM 3. Fabrication of chiral antiferromagnet Mn 3 Ir

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Page 1: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Spintronic operation in antiferromagnets

1CSRN@Osaka Univ.

@Tohoku Univ.

Takahiro MoriyamaInstitute for Chemical Research, Kyoto University

Highlights1. Spin pumping in FM/AFM2. Terahertz spin pumping in AFM3. Fabrication of chiral antiferromagnet Mn3Ir

Page 2: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Magneticsusceptibility

Resonant frequency

FM ~ 103 * A few 10 GHz

AFM ~ 10-2 ** A few THz* Typical value of Fe** Typical value of MnF2

THz dynamics

Ultra high density memoryTolerance to field disturbance

High speed magnetization switchingTHz emission

Small susceptibility

Possibility of antiferromagnetic spintronics

FM memoryBit interference

due to stray field

AFM memoryNo stray field allows 100 times more packed bits*

Close packed memory bits

2

THz emission using antiferromagnetic resonance excited by spin current

THz emission

Spin current

THz

*S. Loth et al., Science 335, 196 (2012).

See reviews in: Jungwirth et al., Nat. Nanotechnol., 11, 231 (2016), and Baltz, TM, et al., RPM 90, 015005 (2018)

Page 3: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Spin current interaction in AFM

(a) Case of FM (b) Case of AFM

How is the spin torque exerting in antiferromagnets?

Well known ?

Page 4: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Spin current dissipation and spin torque

ቤ𝑑𝐦

𝑑𝑡𝑠𝑝𝑖𝑛 𝑡𝑜𝑟𝑞𝑢𝑒

∝ 𝐦 × 𝐦× 𝐏𝐬 ⟹ 𝐏𝐬 sin 𝜃 𝟐 ቤ𝑑𝐦

𝑑𝑡𝑠𝑝𝑖𝑛 𝑡𝑜𝑟𝑞𝑢𝑒

∝ 𝐈 × 𝐈 × 𝐏𝐬 ⟹ 𝐏𝐬 sin 𝜃 𝟐

Gomonay, et al., PRB 81, 144427 (2010)＊in a strong exchange limit

𝐏𝐬 𝐏𝐬

Spin torque

𝐏𝐬′

𝐏𝐬 = spin torque + 𝐏𝐬′

𝐏𝐬′

Spin dissipation in the spin current point of view

=

Ferromagnet Antiferromagnet

𝐈 = 𝒎𝟏 −𝒎𝟐

𝒎𝟏

𝒎𝟐

𝒎

Moriyama, PRL 119, 267204 (2017)

Page 5: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Damping enhancement by spin pumping effect

Damping enhancement as a probe of spin torque effect.

FMNM

Damping 𝛼 of the FM (FMR linewidth) is enhanced due to the spin current dissipation in NM.

FM/NM spin pumping

𝑰𝑠(0)

=𝑔𝑟↑↓

4𝜋𝒎× 𝝁𝒔 ×𝒎

𝛼 ∝ 𝑰𝑠𝑝𝑢𝑚𝑝

− 𝑰𝑠(0)

𝑰𝑠𝑝𝑢𝑚𝑝

=𝑔𝑟↑↓

4𝜋𝒎×

d𝒎

d𝑡

𝝁𝒔

Tserkovnyak, et al. RMP 77, 1375 (2005)

𝑰𝑠𝑝𝑢𝑚𝑝

𝑰𝑠(0)

Cu t nmFeNi 3nmPt 5nm

Mizukami, PRB 66, 104413 (2002)

Gilb

ert

dam

pin

g, G

[1

08

s-1]

Cu thickness (nm)

𝐷𝑎𝑚𝑝𝑖𝑛𝑔 𝑒𝑛ℎ𝑎𝑛𝑐𝑒𝑚𝑒𝑛𝑡 ∝ 1 + 𝑔𝑟↑↓𝑅𝑠𝑑

1 + tanh Τ𝑡𝐶𝑢 λ𝐶𝑢 𝑔𝑅𝑠𝑑tanh Τ𝑡𝐶𝑢 λ𝐶𝑢 + 𝑔𝑅𝑠𝑑

−1

Spin diffusion length: ~250nmλ𝐶𝑢

Page 6: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Damping enhancement with AFM

AFMFM

FM/AFM spin pumping

FM dynamics

Spin pumping injection of Is into AFM

Damping change of FM

Is dissipation in AFM

Damping enhancement as a probe of spin dissipation in AFM.

Can damping enhancement in FM tell the spin dissipation (spin torque) in AFM?

Page 7: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Damping vs. FeMn thickness

Gilb

ert

dam

pin

g, G

[1

08

s-1]

Gilb

ert

dam

pin

g, α

(dim

ensi

on

less

)

FeMn thickness (nm) Cu thickness (nm)

Cu t nmFeNi 3nm Pt 5nm

Mizukami, PRB 66, 104413 (2002)

FeMn t nmFeNi 4nm Pt 5nm

Spin diffusion length of Cu ~250nmSpin diffusion length of FeMn ~100nm

Our results

Spin current carried by spin fluctuation; PRL 113, 097202 (2014).; APL 106, 162406 (2015); PRB 92, 020409R (2015).; PRL 118, 147202 (2017).

𝛼 ∝ 1 + 𝑔𝑟↑↓𝑅𝑠𝑑

1 + tanh Τ𝑡𝐹𝑒𝑀𝑛 λ𝐹𝑒𝑀𝑛 𝑔𝑅𝑠𝑑tanh Τ𝑡𝐹𝑒𝑀𝑛 λ𝐹𝑒𝑀𝑛 + 𝑔𝑅𝑠𝑑

−1

Page 8: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Damping enhancementvs. AFM magnetic structure

AFM twisted

AFM aligned

Any change in spin current dissipation?

FM AFM

FMAFM

ቤ𝑑𝐦

𝑑𝑡𝑠𝑝𝑖𝑛 𝑡𝑜𝑟𝑞𝑢𝑒

∝ 𝐈 × 𝐏𝐬 × 𝐈

Spin dissipation should depend on AFM magnetization direction.

Moriyama, PRL 119, 267204 (2017)

Page 9: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

AFM twisting and damping enhancement

FeMn t nm

FeNi 4 nm Hexchange

Damping is maximized at the relative angle ~180°at which the twisting is maximized.

Exchange couplingInduces a twisting in AFM.e.g. PRL 92, 24 (2004).

φ

Moriyama, PRL 119, 267204 (2017)

∆𝛼

Page 10: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Damping control by temperatureEx

chan

ge b

ias

fiel

d (

Oe)

Mo

re than

half d

rop

!

Damping drastically changes in the temperature range of 300 ~ 400 K. Beneficial for spintronic devices where Joule heating is involved during the operation

(e.g. STT-MRAM)

Moriyama, PRApplied 11, 011001 (2019)

Page 11: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Antiferromagnetic resonance

NiO @ R.T. AFMR

AFMR of NiO bulk

https://www.toptica.com/products/terahertz-systems/

Broadband CW-frequency domain THz spectroscopy

α = 0.0007

TN = 523 K

ω0 = 1.1 THz

T. Moriyama, Phys. Rev. Mater. 3, 051402 (2019)

• High resolution AFMR measurements in THz range

→ Linewidth analysis = damping constant α• Temperature dependence of the AFMR ω = 𝜔0 𝑀0 𝑇

𝑛

TN and 𝜔0~4mm

t = ~3mm

Page 12: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Chiral antiferromagnets: Mn3X

Nakatsuji, Nature 527, 212 (2015).

L12 (fcc): Mn3Pt, Mn3Rh, Mn3Ir

e.g. Chen, PRL 112, 017205 (2014)

DO19 (hexagonal): Mn3Sn, Mn3Ga, Mn3Ge

Ajaya K. Nayak, et al., Sci. Adv. 2, e1501870 (2016).

Measurements on Mn3Ir?

Zhang, PRB 95, 075128 (2017)

Page 13: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Summary

1. Spin pumping in AFM/FM bilayer: Control spin dissipation by the AFM order

FM damping is controlled by AFM

2. Antiferromagnetic spin pumping: Experimentally observed for the first time.

Large 𝑔↑↓ = 43 nm−2 was determined.

3. AHE in Mn3Ir: Positive correlation between S and AH conductivity

AH conductivity is ~40 Ω-1 cm-1

High damping

Low damping

ቤ𝑑𝐦

𝑑𝑡𝑠𝑝𝑖𝑛 𝑡𝑜𝑟𝑞𝑢𝑒

∝ 𝐈 × 𝐏𝐬 × 𝐈APL 106, 162406 (2015); PRB 92, 020409R(2015); PRL 119, 267204 (2017); APEX 11, 073003 (2018); PRApplied 11, 011001 (2019)

PRMatererials 3, 051402 (2019);manuscript under review

manuscript under review

Page 14: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Collaborations & Acknowledgements

Kyoto Univ. Tohoku Univ. U. S. A

Europe

Mr. K. OdaMr. T. IkebuchiProf. T. Ono

Prof. Y. Tserkovnyak (UCLA)Prof. S. Takei (CUNY)

Prof. G. Finocchio (Messina)Prof. M. Carpentieri (Bari)

Prof. M. Kimata

JSPS KAKENHI Gant Nos. 26870300, 17H04924, 15H05702, 16H04487, and 19K21972. Grant-in-Aid for Scientific Research on Innovative Area, ”Nano Spin Conversion Science” (Grant No. 17H05181). Center for Spintronics Research Network (CSRN) research grants. The Kyoto University Foundation.

SPring-8

Dr. T. Okouchi

CSRN@Osaka Univ. @Tohoku Univ.

Gifu Univ.

Mr. K. HayashiProf. K. YamadaProf. M. ShimaProf. Y. Ohya

F u n d i n g s o u r c e s

Page 15: Spintronic operation in antiferromagnets · Damping vs. FeMn thickness 0 8 s-1], α) FeMn thickness (nm) Cu thickness (nm) FeNi 3nm Cu t nm Pt 5nm Mizukami, PRB 66, 104413 (2002)

Thank you for your attention!


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