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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
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)
Spin current interaction in AFM
(a) Case of FM (b) Case of AFM
How is the spin torque exerting in antiferromagnets?
Well known ?
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)
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
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?
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
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)
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
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)
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
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)
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
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
Thank you for your attention!