C u r r e n t - i n d u c e d ma g n e t i z a - PowerPoint PPT Presentation

C u r r e n t - i n d u c e d ma g n e t i z a t i o n d y n a mi c s i n n a n o - ma g n e t T e r u o O n o I n s t i t u t e f o r C h e mi c a l R e s e a r c h , K y o t o U n i v e r s i t y N a n o - ma g n e t s : Wi r e & D i s k Magnetic vortex in disk Domain wall in nanowire 1

I n s t i t u t e f o r C h e mi c a l R e s e a r c h D i v i s i o n o f Ma t e r i a l s C h e mi s t r y N a n o s p i n t r o n i c sL a b . 2

A c k n o wl e d g me n t s P. Fischer (LBNL) A.Thiaville (Paris-sud.) Y. Nakatani (UEC) H. Kohno (Osaka) G. Tatara (Metropolitan) 3

Magnetics to Spintronics Data writing : changing the magnetization direction Conventional : magnetic field produced by current flow (discovered by Ørsted in 1820) Not efficient: field spread out, non-local method N Use of coupling between charge and spin! - e Local and efficient writing 4 S

Current-driven domain wall motion (Action-reaction law) D o m a i n w a l l Static domain wall C u r r e n t Spin rotates anti-clockwise. Action-reaction! Local magnetic moment should rotates clockwise. DW motion by electric current without magnetic field!! 5

Sample for a single DW injection 240 nm Ni 81 Fe 19 (10nm) H DW inj ect or K. Shiget o et al.,Appl. Phys. Let t . 75 (1999) 2815. 6

MFM observation of current-driven domain wall motion (head-to-head domain wall) + Current ( 7 × 10 11 A/m 2 , 5µs ) H 1 A 7 ×1 0 / m , 5 µ s 1 2 - Current ( 7 × 10 11 A/m 2 , 5µs ) Ni 81 Fe 19 wire widt h: 240 nm t hickness: 10 nm 1 A 7 ×1 0 / m , 5 µ s 1 2 D W m o v e s o p p o s i t e t o c u r r e n t d i r e c t i o n , 7 d i r e c t i o n o f e l e c t r o n f l o w .

Current-driven domain wall motion (tail-to-tail domain wall) + Current ( 7 × 10 11 A/m 2 , 5µs ) H 1 A 7 ×1 0 / m , 5 µ s 1 2 - Current ( 7 × 10 11 A/m 2 , 5µs ) 1 A 7 ×1 0 / m , 5 µ s 1 2 T a i l - t o - t a i l D W a l s o m o v e s o p p o s i t e t o c u r r e n t d i r e c t i o n . 8

Successive images of DW motion by current pulse injections (7 × 10 11 A/m 2 , 0.5 µs) NiFe, w = 240nm, t = 10nm Phys. Rev. Let t ., 92 (2004) 077205. D W p o s i t i o n c a n b e c o n t r o l l e d b y c u r r e n t p u l s e d . 9

Field-driven v.s. Current-driven DW motion Ma g n e t i c f i e l d - d r i v e n D W mo t i o n … . D W s a n n i h i l a t e e a c h o t h e r E l e c t r i c c u r r e n t - d r i v e n D W mo t i o n D W s a r e m o v i n g t o g e t h e r t o t h e s a m e d i r e c t i o n . I n f o r m a t i o n ( D W ) c a n b e t r a n s f e r r e d ! 10

Magnetic Racetrack Memory proposed by IBM A n o v e l t h r e e - d i me n s i o n a l s p i n t r o n i c s t o r a g e me mo r y Magnetic nanowires: information stored in the domain -Capacity of a hard disk drive -Reliability and performance of solid state memory (DRAM, FLASH, SRAM...) 11 Courtesy of Stuart Parkin (IBM)

Activities of DW devices in Japan Fujitsu NEC セル構成図（ セル構成図（ 例） 例） T M R 素子 T M R 素子 読出し電流 読出し電流 読出し電流 BL BL BL BL BL BL BL BL GND GND GND 書込み電流 書込み電流 書込み電流 WL WL WL WL Storage Fast MRAM Replace SRAM Post HDD NEDO Spintronics nonvolatile devices project 12

What is magnetic vortex? C u r l i n g s p i n s t r u c t u r e t o r e d u c e t h e m a g n e t o s t a t i c e n e r g y . H o w e v e r , a t t h e c e n t e r o f t h e d i s k , t h e e x c h a n g e e n e r g y i n c r e a s e s w i t h d e c r e a s i n g t h e a n g l e b e t w e e n n e i g h b o r i n g s p i n s . M a g n e t o s t a t i c e n e r g y v . s . E x c h a n g e e n e r g y V o r t e x c o r e w i t h m a g n e t i z a t i o n p e r p e n d i c u l a r t o d i s k p l a n e ! 2 ) 1/ 2 ～ 5nm m z ~ exp[-( r / ξ ) 2 ] , ξ = (2 µ 0 A / M s M F M , N M F M , N i F ed d i s k i F e i s k V o r t e x c o r e m e m o r y “0” “1” T . S h i n j o e t a l . , S c i e n c e , 13 H o w t o wr i t e a n d r e a d ? 2 8 9 ( 2 0 0 0 ) 9 3 0 .

Resonance of vortex core by AC current -Micromagnetic simulation including spin transfer term- ∂ µ m g JP = − γ × + α × − u ∂ = & & B m m H m m , u 2 eM x s I exc = 3 × 10 11 A/m 2 ( P =0.7) D= 500nm, t=40nm Radius of steady orbital (nm) t = 40 nm Ni 80 Fe 20 I ex I ex =3 × 10 11 A/m 2 Experimental proof: Resistance measurements, Kasai et al., PRL 97, 107204 (2006). 14 X-ray microscope, Kasai et al., PRL 101, 237203 (2008).

Vortex core motion by AC current with high current density I ex = 4 × 10 11 A/m 2 D=500nm, t=40nm I ex V o r t e x c o r e s w i t c h i n g b y c u r r e n t ! 15

Observation of Current-induced core switching （ １ ） （ ２ ） I exc （ ３ ） （ 1 ） C h e c k c o r e d i r e c t i o n （ 2 ） E x c i t a t i o n （ 3 . 5 ×1 0 A / m , 2 9 0 M H z ） 1 1 2 （ 3 ） C h e c k c o r e d i r e c t i o n （ 4 ） C o n t i n u e t h i s p r o c e s s Yamada et al., Nature Materials 6, (2007) 270. mA c u r r e n t c a n s wi t c h t h e c o r e ! s wi t c h i n g b y s t a t i c f i e l d ～ s e v e r a l k O e 16 C o r e s e e ms t o s wi t c h r a n d o ml y ? !

P r o b l e m s o f V C s w i t c h i n g b y r e s o n a n c e ( 1 ) L o n g s w i t c h i n g t i m e o f s e v e r a l t e n s n s ( 2 ) P o o r c o n t r o l l a b i l i t y o f V C d i r e c t i o n C r i t i c a l c o r e v e l o c i t y f o r s w i t c h i n g C r i t i c a l v e l o c i t y S a m e c r i t i c a l v e l o c i t y r e g a r d l e s s o f t h e c u r r e n t d e n s i t y . C o r e v e l o c i t y ( n o t c u r r e n t d e n s i t y ) i s e s s e n t i a l ! 17 C u r r e n t p u l s e w i t h h i g h e r c u r r e n t d e n s i t y !

Core switching by current pulse 1.3 × 10 12 A/m, 2.5 ns K. Yamada et al ., Appl.Phys.Lett., 93, 152502 (2008). N i F e d i s k , D = 1 5 5 0 n m , t = 5 5 n m ・ O n e s h o t s w i t c h i n g b y n s c u r r e n t p u l s e ! ・ P r e c i s e c o n t r o l o f v o r t e x c o r e d i r e c t i o n ! 18

M T J f i l m & s a m p l e s t r u c t u r e MR curve Ru(2) PtMn(15) ∆ R = 0 . 91 CoFe(2.5) R Pinned-layer Ru(2) Pillar size 18x9 µ m 2 CoFe(1.5) CoFeB(1.0) MgO(1.4) CoFeB(2) SEM image of the sample Free-layer V o u t Permalloy(20) Ta(5) Si/SiO2 V i n Synthesized by NEC 19 3-terminal devise

V o r t e x t r a n s i s t o r w i t h M T J output input V o u t Output signal is obtained for resonance frequency. V i n The signal is tuned by bias-voltage to MTJ. S. Kasai et al ., Appl. Phys. Express 1(2008) 091302. 20

Summary D o ma i n wa l l V o r t e x c o r e C u r r e n t - i n d u c e d d y n a mc s D W v e l o c i t y , S c i e n c e ( 1 9 9 9 ) V o r t e x c o r e , S c i e n c e ( 2 0 0 0 ) P h y s . R e v . L e t t . ( 2 0 0 6 ) C o r e r e v e r s a l b y c u r r e n t , C u r r e n t - d r i v e n D W mo t i o n , N a t u r eMa t e r i a l s ( 2 0 0 7 ) P h y s . R e v . L e t t . ( 2 0 0 4 ) 21

22 ! u o y k n a h T